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BIOHSC43457 P0027599

BiologyHSC CourseStage 6

Communication

Incorporating October 2002

AMENDMENTS

AcknowledgmentsThis publication is copyright Learning Materials Production, Open Training and Education Network –Distance Education, NSW Department of Education and Training, however it may contain material fromother sources which is not owned by Learning Materials Production. Learning Materials Productionwould like to acknowledge the following people and organisations whose material has been used.

• Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. AmendedNovember 2002

All reasonable efforts have been made to obtain copyright permissions. All claims will be settled ingood faith.

Writer Jane West and Steve Vassallo

Editor Ric Morante

Illustrator Thomas Brown

Photographs Thomas Brown

David Stanley

Jane West

Layout Gayle Reddy

Copyright in this material is reserved to the Crown in the right of the State of New South Wales.Reproduction or transmittal in whole, or in part, other than in accordance with provisions of theCopyright Act, is prohibited without the written authority of Learning Materials Production.

© Learning Materials Production, Open Training and Education Network – Distance Education,NSW Department of Education and Training, 2003. 51 Wentworth Rd. Strathfield NSW 2135.

Introduction i

Contents

Module overview

Outcomes ............................................................................................ iii

Indicative time...................................................................................... iii

Resources............................................................................................ iii

Icons .....................................................................................................v

Glossary............................................................................................... vi

Part 1: Making sense of your surroundings.........................1–35

Part 2: Eye can see clearly .................................................1–29

Part 3: I can see the light ....................................................1–30

Part 4: Making sounds ........................................................1–24

Part 5: What’s this ear?.......................................................1–37

Part 6: It’s all in the head.....................................................1–34

Student evaluation of the module

ii Communication

Introduction iii

Module overview

Humans are great communicators. Every waking hour of the day there isa flood of information received by the senses. Some of these senses,such as sight and hearing, play an important role in communication inhumans. Other organisms use sensory information that cannot bedetected by humans for communication. The brain plays an importantrole in the interpretation of this information and controls behaviour.

Outcomes

This module increases students’ understanding of the history,applications and uses of biology, implications of biology for societyand the environment and current issues, research and developmentsin biology.

Indicative time

This module is divided into six parts. You need to spend at least fivehours on each part. Therefore, the module Communication is designedso that you should take at least thirty indicative hours to complete.

Resources

Part 1:

• one single-edged razor blade or knife

• scalpel

• scissors

• paper towel

iv Communication

• plastic garbage bags

• rubber gloves.

Part 2:

• hard clear plastic or glass

• water

• newspaper

• two convex lenses

• light source.

Part 6:

• microscope and prepared slides of neurones

• a sheep’s brain from the butcher or abattoir

• scalpel or knife

• rubber gloves

• newspaper

• cutting board.

Introduction v

Icons

The following icons are used within this module. The meaning of eachicon is written beside it.

The hand icon means there is an activity for you to do.It may be an experiment or you may make something.

You need to use a computer for this activity.

Discuss ideas with someone else. You could speak withfamily or friends or anyone else who is available. Perhapsyou could telephone someone?

There is a safety issue that you need to consider.

There are suggested answers for the following questionsat the end of the part.

There is an exercise at the end of the part for you tocomplete.

You need to go outside or away from your desk for thisactivity.

vi Communication

Glossary

The following words, listed here with their meanings, are found in thelearning material in this module. They appear bolded the first time theyoccur in the learning material.

accommodation changing the focus in the eye by changing theshape of the lens using the ciliary muscles

action potential reversal of voltage across a nerve membranecaused by the movement of sodium andpotassium ions

acuity sharpness of vision

aqueous humour transparent fluid that lies between the corneaand the lens

axon an extension on a neurone that takes theimpulse away from the cell body

binocular involving the use of two eyes with overlappingfield of view resulting in depth perception

bioluminescence the production of light by living organisms

blind spot the place on the retina where the optic nerveleaves the eye, contains no light sensitive cells

cataract a clouding of the eye’s lens

cell body part of the neurone that contains the nucleusand other organelles

cetaceans order of marine mammals

choroid a layer between the sclera and the retina

ciliary body contains the suspensory ligaments and theciliary muscles in the eye

cilary muscles small muscles attached to the lens that changethe shape of the lens to focus on near and farobjects

colour blind inability to detect particular colours caused bya lack of specific colour cone cells

cone cell light sensitive cell found on the retina of theeye, particularly important in colour perception

conjunctiva membrane lining the outer layer of the eye

cornea transparent layer at the front of the eye,refracts incoming light

Introduction vii

dendrite extension of a neurone that transmits the signaltowards the cell body

effector a muscle or gland that produces a response to astimulus

fovea point on the retina with the greatest acuity andthe greatest number of cone cells

incus one of three small bones in the middle ear

ion a charged atom or group of atoms

iris coloured part of the eye, controls the amountof light entering the eye

labyrinth organ in the inner ear that is responsible forbalance

lateral line a visible line along the head and body of fishand amphibians, senses low frequency sound

malleus first of three small bones in the middle ear

mechanoreceptors a receptor that responds to sound, pressure,touch and position

monocular vision from one eye

myelin sheath a mixture of fat and proteins that acts as aninsulator around neurones

nerve a bundle of neuronal fibres

neuromasts sensory cells found in the lateral line organ offish and amphibians

neurone a single nerve cell

neurotransmitters chemicals that transmit the nerve impulse inthe synapse between two neurones

ocellus/ocelli simple eye spot

ommatidia visual units of the compound eye ofinvertebrates

optic nerve nerve that leaves the retina of the eye

otolith calcareous mass found in the ear of somevertebrates, important in sound perception infish

oval window the connecting plate between the middle earand inner ear

peripheral on the outer side

pheromones chemicals released as a signal

viii Communication

photoreceptor an organ or cell, sensitive to light

pitch function of the frequency of a wave, high orlow sounds have high or low pitch

polarisation separation of positive and negative ions

pupil the opening in the iris of the eye

receptors detect changes in the environment

recessive not expressed in the phenotype unless it is theonly gene present

refraction bending of light

refractory period the time taken for a neurone to recover afterfiring

resting potential the normal state of a neurone, negativelycharged internally

retina light sensitive lining on the back of the eye

rhodopsin light sensitive pigment found in rod cells

rod cells light sensitive cells especially useful for thedetection of low light

Schwann cells a type of cell that produces the myelin sheatharound nerve cells

sclera tough white coating in the eye

sex-linked a gene found on one of the sex chromosomes

sound shadow the acoustic shadow cast by the head, used inthe localisation of sound

spike graphical interpretation of the firing of aneurone

stapes the third bone in the middle ear

stereocilia hair-like extensions on hair cells that contactthe tectorial membrane and send an impulse tothe brain

stereoscopic three dimensional view using the overlappingfield of view from two eyes

stimuli an external message that excites a receptor

stimulus singular of above

synapse the gap between two neurones

syrinx the voice box of birds

Introduction ix

threshold a level of intensity necessary to fire a neurone

transparent clear, see through

tympanic organ a hearing organ found in insects that is similarin structure to the mammalian eardrum

vitreous humour jelly-like substance that fills the eye betweenthe lens and the retina

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Communication

Part 1: Making sense of your surroundings


AMENDMENTS

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Part 1: Making sense of your surroundings 1

Contents

Introduction ............................................................................... 2

The role of receptors ................................................................. 4

Detecting stimuli ...................................................................................4

Response to a stimulus........................................................................5

Senses in communication ......................................................... 7

Communication ....................................................................................7

Visual communication ............................................................. 12

Anatomy and function of the human eye .........................................12

Investigation of a mammalian eye ....................................................15

Detection of energy ................................................................. 20

Vision range........................................................................................22

Summary................................................................................. 25

Suggested answers................................................................. 27

Additional resources................................................................ 29

Exercises – Part 1 ................................................................... 31

2 Communication

Introduction

Spend a couple of minutes thinking about what you are sensing at themoment. If you are reading this page your eyes are sending messages tothe brain based on the symbols it recognises on the page. What soundsdo you here? Do you feel hot or cold? What are your immediate smelland/or taste sensations?

Humans and other animals are able to detect a range of stimuli (inputs)from the environment. Which ones are useful for communication?What senses are you using when you communicate to another human?Is it the same as the senses used by other animals?

This part of the module identifies the range of senses involved incommunication. You will look at specific examples of communication inhumans and other animals.

You will be asked to dissect a mammalian eye during this part of themodule. To do this you will need to get an eye from your local butcheror abattoir. As well as the eye you will need scissors, paper towelsand a single-edged razor blade, knife or scalpel. Alternative activitiesare supplied.

In this Part you will be given opportunities to learn to:

• identify the role of receptors in detecting stimuli

• explain that the response to a stimulus involves:

– stimulus

– receptor

– messenger

– effector

– response.

• identify the limited range of wavelengths of the electromagneticspectrum detected by humans and compare this range with those ofother vertebrates and invertebrates

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• describe the anatomy and function of the human eye, including the:

– conjunctiva

– cornea

– sclera

– choroid

– retina

– iris

– lens

– aqueous and vitreous humour

– ciliary body

– optic nerve.

In this Part you will be given opportunities to:

• identify data sources, gather and process information from secondarysources to identify the range of senses involved in communication

• plan, choose equipment or resources and perform a first-handinvestigation of a mammalian eye to gather first-hand data to relatestructures to functions

• use available evidence to suggest reasons for the differences in rangeof electromagnetic radiation detected by humans and other animals.

Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originallyissued 1999. Amended November 2002. The most up-to-date version can befound on the Board’s website at:http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html

4 Communication

The role of receptors

Signals from the environment detected by our sense organs are calledstimuli (singular stimulus). These signals may be in the form ofvibrations, light and even changes in temperature. Organisms haveevolved special senses to detect stimuli and some of these senses are usedin communication. Animals use a range of different receptors to receivemessages involved in communication.

Detecting stimuli

Communication is a message requiring a sender and a receiver.

You observe the environment around you using your senses. Can youremember all the senses that humans possess? See if you can listthem below.

_________________________________________________________

_________________________________________________________

You sense your environment through the use of your sense organs.Now try to list as many sense organs as you can in the space below.

_________________________________________________________

_________________________________________________________

Check your answers

Our sense organs contain receptors that convert the stimulus from theenvironment to a nerve impulse that goes to the brain. Receptors arespecialised cells. Their role is to detect stimuli. Each type of senseorgan contains a different kind of receptor.

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The receptor in the eye is called a photoreceptor because itresponds to light.

The sense of touch is actually made up of a number of different kinds ofreceptors varying in size, shape, number and distribution within the skin.They are responsible for relaying information about pressure,temperature and pain.

The table below summarises the stimuli, receptors and organs foundin humans.

Sense organ Receptor type Stimulus

eye photoreceptors light (visible)

nose chemoreceptors chemicals

tongue chemoreceptors chemicals

skin mechanoreceptors

thermoreceptors

pressure, touch

heat (infra-red)

ear mechanoreceptors

hair cells

semicircular canals

sound

gravity

Some of these are more important than others for communication.

Response to a stimulus

Once a receptor detects a stimulus it sends a message along a nervouspathway in the form of an electro chemical impulse. The nervouspathway consists of a sensory neurone (a nerve cell often spelt neuron)that sends the message to the connecting neurones in the central nervoussystem (CNS) of the brain and spinal cord. From here it travels to themotor neurone that transfers the message to effector organs such asmuscles or glands. You will learn more about this in Part 6 ofthe module.

The impulse that travels through nerves is called the messenger. Once itreaches the effector (in the muscle or in some cases a gland) the messagecauses a reaction called a response.

6 Communication

The response to a stimulus can be demonstrated by the ‘knee jerk’ reflexshown below.

Try this on a friend and/or have it done to you. Tap the knee gently in theposition shown in the diagram. You may have to try a few times until youhit the right spot. The knee should jerk upwards in response.

The response to a stimulus can be summarized as follows:

motor neurone

sensory neuronereceptor

stimulus

messenger

effector

response

Do Exercise 1.1 now.

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Senses in communication

You have just learnt that a sensory receptor enables you to detectstimuli and the mechanism whereby it causes a response. This sectionwill deal with how these actions are used in communication.Remember communication occurs between a sender and a receiver.

Communication

Information communicated about the various parts of an organism’ssurroundings helps to construct a perception of its environment thataids survival.

In biological terms communication means transferring or transmittinga signal from one organism to another. This can be by means of sound,visual signals, taste or smell, electrical impulse, touch or acombination of these.

Living organisms are always communicating with each other whether itis between members of different species or among members of the samespecies. Communication is not limited to animals. Most floweringplants communicate with animals to aid pollination and reproduction.

Animals use a range of senses to communicate a desire to mate with theopposite sex, gather food and defend territory.

Range of senses used in communication

Humans have five senses, touch, taste, smell, sight and hearing.Animals are not limited to only these senses. Each species relies ondifferent senses and has different depths of perception.

8 Communication

Examples of animal senses

Some examples of animal senses not shared by humans are:

• echolocation

• lateral line systems

• Jacobsen’s organ

• electric field detection.

Echolocation

Dolphins, whales and bats use this form of hearing to communicate andto navigate. Dolphins produce 700 clicks per second and can locateobjects hundreds of metres away by this method. A bat flying silentlyacross the night sky is actually using sound to navigate but we are unableto detect the sound.

Lateral line systems

Many fish have a line that runs the length of their body that is able todetect changes in water pressure. It helps them feel movements in thewater around them.

(Photo: Jane West)

Jacobsen’s organ

This organ is found in snakes. It is located on the roof of the mouth.The snake’s forked tongue collects chemicals from the air and pressesthem into the organ.

Electric fields

Sharks and some fish track prey by the weak electric fields created inwater. The platypus has electroreceptors in its bill. It uses weak electricfields to locate prey. The African Electric fish is nocturnal and lives inmurky water. It sends out 300–400 pulses of electricity per second.It can detect any change in the electric field to locate prey.

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Communicating with the senses

Not all senses are used in communication, however the main senses usedin communication are:

• hearing (auditory)

• sight (visual)

• smell (olfactory)

• touch (tactile).

Auditory

Often if you go for a walk in the bush you will hear the sounds of manyanimals. Usually it is the sounds of animals rather than the sight of themthat is obvious. In the early morning and evening many birds and insectscall to communicate. They may be declaring their territory, alertingothers of a predator or searching for a mate. There are even many soundsthat you can’t hear such as the ultrasonic call of some moths and bats.

An advantage of auditory signals is that the message can travel greatdistances. For example, howler monkeys and siamangs call through thetropical forests declaring their territory. Another advantage of soundcommunication is there is no need to be close to communicate by sound.

Visual

Visual displays include body posture, colour, facial expression andthreatening behaviour. The plumage of birds is used in displayand courtship.

A male gorilla will defend his territory by beating his chest and makingaggressive movements. This visual display scares off intruders withoutthe need for actual physical violence.

Birds use visual displays to great effect. They have four types of colourreceptors on their retinas, one more type than humans. They can seecolour in another dimension. This may explain why some birds havecolourful plumage.

Smell

Olfaction (the sense of smell) is one of the oldest senses in evolutionaryterms. It is the detection of chemicals in the environment. This ability isused by predators to locate prey and by prey to escape predators.

10 Communication

Many animals use the sense of smell to find sexual partners and to avoidpredators. Scent marking is used to declare territories.

Human sense of smell is limited but animals such as dogs live in a worldof smells. If you have taken your dog for a walk you would have noticedhow interested the dog is in all the smells that abound. Dogs mark theirterritory by urinating on prominent objects. They can tell if a female dogis on heat by the odour given off.

The chemicals that carry messages are called pheromones. They aresignaling molecules. They can tell an individual’s identity. For insectschemical communication is highly developed. A male moth can detect afemale moth more than a kilometre away. The amount of pheromone canbe very small. In the case of the moth the male only requires to detectone molecule of the female pheromone to fly off and find her.Queen bees give off pheromones that prevent the worker beesbecoming sexually mature.

Ants communicate in many ways using pheromones. In ant coloniespheromones are used to trigger attacks, set trails, exchange food, defendtheir territory and control reproduction. Insect pheromones are sopowerful that they are used to control pest species in agriculture.Female pheromones are released over crops to confuse and overload themales with stimuli and prevent mating.

Insects have olfactory organs on their antenna to detect odours.Some have more than 100 000 sensory hairs. Rodents have powerfulresponses to pheromones. The golden hamster will give up matingcompletely if the olfactory part of the brain is removed.

Tactile

When animals use the sense of touch they are close together.Therefore it is used in fighting and in courtship behaviour.Many mothers and infants communicate by touching.

Touching is very important in communicating group bonding especiallyin primates. Chimpanzees greet each other by shaking hands.They groom each other for hours. Horses rub noses apparently toshow affection.

Bees dance to communicate the location of a food source. They giveinformation on both the distance and direction. This occurs in thedarkness of the hive.

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Taste

Poisonous animals sometimes have an unpleasant taste to communicateto a predator that they are not to be eaten. Humans do not use taste as aform of communication.

Identify data sources, gather and process information from secondarysources to identify the range of senses used in communication.

Hint

Find a data source to identify the range of senses used in communication.This could be on the Internet, a book or a popular scientific journal.Identify the data source using the referencing system given in theAdditional resources section at the back of this part.

Write the reference that you have found in the space below.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Summarise the information above by placing it in the table in Exercise 1.2.

12 Communication

Visual communication

By far the most important sense organ in humans is the eye. Not only isthe detection of light images important for survival but also theperception of colour and depth are absolute necessities for some animals.Visual communication involves the eye registering changes in theimmediate environment.

Anatomy and function of thehuman eye

The structure of the eye is delicate and complex. It makes sense ofthe light stimuli streaming into it every waking hour of the day.The anatomy of the eye consists of three layers. The outer layerconsists of the sclera which surrounds the eye and the cornea at thefront of the eye.

(Photo: Jane West)

retina

sclera

cornea

The sclera is the dense white layer of the eye. It protects the eye.The cornea is the clear jelly-like front of the eye. It protects the front ofthe eye and focuses light entering the eye.

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The middle area of the eye consists of the dark pigmented choroid layer.This membrane layer prevents light from scattering by absorbing light.It contains the blood vessels that nourish the eye. Suspended from thechoroid layer is the pigmented iris. The iris is a muscular structure thatcontrols the amount of light that enters the eye by changing the size ofthe pupil. The pupil is the hole in the centre of the iris.

Behind the iris is the lens which consists of layers of transparentproteins. The lens is responsible for the fine focus of light on to the backof the eye. The lens is moved by the ciliary muscles. The ciliarymuscles and the suspensory ligaments are located in the ciliary body thislinks the choroid to the lens. In front of the lens is a clear watery fluidcalled the aqueous humour (also spelt aqueous humor). This fluidtransmits light and maintains the pressure of the eye. Behind the lens inthe centre of the eye is the vitreous humour (vitreous humor).This jelly-like substance allows light to travel through to the back of theeye and maintains the shape of the eye. The conjunctiva is acontinuation of the epidermis, it covers the surface of the eye andprotects the cornea.

conjunctiva

iris

pupil

ciliary body

lensretina

vitreous humour

aqueoushumour

choroid

The inner layer of the eye consists of the retina, which detects light withlight sensitive cells (photosensitive), the fovea the area of greatest visualacuity and the start of the optic nerve. The optic nerve carries thenervous impulses from the retina to the visual cortex in the brain.Where the optic nerve leaves the retina is the blind spot. There are nophotoreceptors at that point.

14 Communication

retinafovea

blind spot

optic nerve

retina

Optional activity: test your blind spot

You can find your blind spot by performing this activity using thediagram below. Cover your left eye and stare at the cross. You will beable to see the circle in the periphery of your view. Don’t look at thecircle. Move the page in and out as you look at the cross. The circle willdisappear when the image of the circle is focused on the blind spot.Try the same with the other eye. This time cover your right eye and lookat the circle.


Visit the LMP Science Online webpage for this module to see an interactiveversion of the eye diagram at: http://www.lmpc.edu.au/science

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Investigation of a mammalian eye

You have been reading about the structure of an eye now it’s your chanceto examine one in more detail.

Plan, choose equipment or resources and perform a first-hand investigationof a mammalian eye to gather first-hand data to relate structure to functions.

Hint

Plan your experiment and choose your equipment or resources from thematerials you have available to you. Predict possible issues that mayarise during the experiment. In this case there is a risk assessmentnecessary to predict the dangers of using sharp instruments. Address thepotential hazards that may occur. Plan what you will do with wastematerial from the experiment and have equipment such as a disposalplastic bag ready to be used. As you do the dissection try to relate thestructures that you are seeing to the function they perform in the eye.

If you are unable to do the dissection then use the photographs below or seethem in colour at the LMP Science Online web site for this module at:http://www.lmpc.edu.au/science

Planning

You can order cow’s eyes at a butcher shop or purchase them directlyfrom abattoirs. Try to get eyes with the muscles and fat still attached.If possible pick up the cow’s eyes the day of the dissection; eyes areeasier to cut when they are fresh.

There are some risks to assess in this activity. You will be dealing withanimal tissue so make sure that you wear rubber gloves. You will also beusing sharp instruments so be aware of the dangers of cutting yourself.When you have finished dispose of any waste by wrapping in paper and thenplace in a plastic bag before placing in the garbage bin. Wear appropriateclothing including covered footwear during the activity. Risk of anyinfection from the material is very unlikely. In some overseas countrieswhere BSE (bovine spongiform encephalitis or mad cow disease) iscommon there may be a slightly higher risk of infection and more care isneed to be taken with the disposal of the material.

16 Communication

Materials required:

• one single-edged razor blade, knife or scalpel

• scissors (optional)

• paper towels

• plastic garbage bag

• rubber gloves.

Procedure

Examine the outside of theeye. See how many parts ofthe eye you can identify.

You should be able to findthe whites (or sclera)

and the clear covering overthe front of the eye (thecornea). The conjunctiva isthe outer membrane coveringthe cornea.

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You should also be able toidentify the fat and musclesurrounding the eye.

Return your attention to theoutside of the eye. Locatethe optic nerve. To see theseparate fibers that make upthe optic nerve, pinch thenerve with a pair of scissorsor with your fingers.

Make the first incision wherethe sclera meets the cornea.Cut until the aqueous humouris released. Rotate the eyeand cut around the cornea.Be careful not to cut too deepor you may cut the lens. Asthe cornea starts to comefree, hold the cornea in thecentre and make the last cutsaround it.

Once you have removed thecornea, place it on the board(or cutting surface) and cut itwith your scalpel or razor.

With the cornea removed, thenext step is to pull out theiris. Place one finger in thecentre of the eye. Find theiris and pull it back. Itshould come out in onepiece.

18 Communication

It can be a bit tricky toremove the lens with thevitreous humour attached. Itworks best if you cut slits inthe sclera. Be careful not tocut the lens.

After enough incisions havebeen made in the sclera, youshould be able to remove thelens. Sometimes the vitreoushumour will be removedalong with the lens. Hold upthe lens and look through it.If the lens is too slippery, patit dry with the paper toweland try again.

With the vitreous humournow removed, you should beable to turn the eye insideout.

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The thin tissue on the back ofthe eye is the retina. Find theblind spot where the opticnerve is attached.

Results

Draw a diagram of your dissection (or use the one above) in the spacebelow. Show the optic nerve, cornea, sclera, lens, retina and theblind spot.

Conclusion

Describe the functions of each structure of the eye, and hoe eachstructure is suited to perform that function.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

20 Communication

Detection of energy

An animal senses light using the properties and specialised nature oflight. The light detecting receptors of the eye (called photoreceptors)can pick up certain wavelengths of energy which we call visible light.To understand more fully how animals detect and communicate lightyou must first learn a bit about the nature of this peculiar type of energy.

Light comes from various sources. Can you list some?

The most important source is the sun. Things like fire, electric lights andglowing hot objects all produce light. Some animals produce light.This is known as bioluminescence.

Light is a form of electromagnetic radiation (EM). Light energy issimilar in lots of ways to other forms of energy like heat, ultravioletradiation, microwaves and X-rays.

The diagram below shows how these various forms of energy aredistinguished by their wavelengths (measured in nanometres, nm).

10–11 10–9 10–7 10–5 10–2 100 103 106

0.01 nm 1 nm 0.1 mm 0.01 mm 1 cm 1 m 1 km 103 km

gammarays

x-rays ultraviolet infra-redmicrowaves

0.4–0.7mm

light TV radioradio waves electrical

power

Wavelength

Wavelength in metres

The diagram shows that energy is made up of vibrating waves of variouswavelengths. Each wavelength represents a different kind ofelectromagnetic radiation. Even light energy is a mixture of differentwavelengths we call colour. Violet light waves are about 380 nm whilered light waves are larger at about 700 nm. Below 380 nm is ultravioletand above 700 nm is infra-red neither of these is visible to humans.Human vision is limited to the visible light range.

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White light is a combination of what is perceive as coloured light.In 1666 Isaac Newton separated white light into the spectrum of coloursusing a glass prism demonstrating that white light is made up of amixture of colours.

prism

0.4 0.5 0.6 0.7

red

yello

wgr

een

blue

indigo

violet

10-5 10-3 10-1 101 103 105 107 109 1011 1013 1015 1017

gammarays

x-raysrays

ultravioletrays

infraredrays radar broadcast bands AC circuits

You can view this diagram in colour on the LMP Science Online web sitefor this module at: http://www.lmpc.edu.au/science

The range of colour vision that humans perceive is from 390 to 750 nm.It is very important at this stage for you to understand that the human eyeonly senses the range of colour vision from violet to red. Violet light hasthe shortest wavelength and the most energy while red light has a longerwavelength. The most effective wavelength for human vision is around500 nm, which is blue-green light.

Wavelength of light (nanometres) Colour

Less than 390 non-visible ultraviolet

390 violet

450 blue

500 blue-green

550 green

570 yellow

600 orange

750 red

Greater than 750 non-visible infra-red

22 Communication

What is the limited range of wavelengths detected by humans?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

Vision ranges

It is important for you to know that not all animals perceive the samerange of wavelengths of electromagnetic radiation as people. The rangeof wavelengths that is biologically important for vision is 300–850 nm.Above 850 nm there is not enough energy to excite the photoreceptorsand below 300 nm the amount of energy is so great that it can destroy thesensitive photoreceptors.

Many arthropods such as bees, ants and spiders and some vertebratessuch as the Japanese Dace fish, carp and goldfish use the ultravioletrange (300 to 400 nm) for vision. Butterflies and other flying insects cansee landing lines on flowers using UV vision. To human vision thelanding strips are invisible.

Sharks have almost no colour vision. Sea turtles have good vision forreds and yellows but not for blues and greens. Dogs see muted colourbut make up for this with greater movement sensitivity and night vision.Snakes can see in two ways. Firstly they have their eyes to see using thevisual range and then they have infra-red receptors located in pit organs.These pit organs are usually located on the head or along the jaw.They are sensitive to heat given off by other animals. It allows them tolocate prey even in the dark.

To see the world through infra-red receptors visit the LMP Science Onlineweb site for this module at: http://www.lmpc.edu.au/science

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So, there is a range of wavelengths that are detected by animals rangingfrom the ultraviolet to the infra-red. The table below summarises someof this information.

Organism Example Wavelengthrange(nanometres)

Part of theEMspectrum.

bee 340–540 UV andvisible

invertebrate

ant 340–540 UV andvisible

human 390–750 visible

carp 360–700 UV andvisible

pit viper 400–850 infra-red andvisible

deep seafish

470–480 visible

vertebrate

pigeon 360–500 near UV andvisible

Do exercise 1.4 now to complete this first part of the module.

24 Communication

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Summary

During this part of the module you should have carried out the followingfirst-hand investigations and other tasks using secondary information.

First hand investigations

Make sure you can describe how you did the following first-handinvestigations. List the precautions that need to be taken during theexperiments and the safe working practices you used.

• Plan, choose equipment or resources and perform a first-handinvestigation of a mammalian eye to gather first-hand data to relatestructures to functions.

Secondary information• Identify data sources, gather and process information from

secondary sources to identify the range of senses involved incommunication.

• Use available evidence to suggest reasons for the differences inrange of electromagnetic radiation detected by humans and otheranimals.

Summary of content• Communication is the transfer of information from a sender to a

receiver.

• Receptors are specialised cells whose role is to detect stimuli.

• Examples of receptors are photoreceptors (light), chemoreceptors(chemicals) and thermoreceptors (temperature).

• Some receptors are used in communication.

26 Communication

• A stimulus – response pathway is:

stimulus receptor messenger effector response

bright light sensory cellsin eyes

nerve muscle

musclecontracts

• The electromagnetic spectrum visible to humans ranges from390–750 nm.

• Other organisms such as snakes can see into the infra-red range,insects can see ultraviolet light.

• The structure of the eyes consists of the conjunctiva, cornea, sclera,choroid, retina, iris, lens, aqueous and vitreous humour, ciliary bodyand optic nerve.

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Suggested answers

Here are suggested answers for many of the questions fromthroughout this part. Your answers should be similar to these answers.If your answers are very different or if you do not understand an answer,contact your teacher.

Detecting stimuli1 Human senses are sight (visual), hearing (auditory), smell

(olfactory), touch (tactile) and taste (gustatory).

2 The human sense organs are eyes, ears, nose, skin and tongue.

Detection of stimuli

The range of human vision is from violet to red in the visible spectrum.The wavelength of waves is 390 to 750 nanometres.

28 Communication

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Additional resources

Citing References

There are certain standard ways of writing a reference list. Here aresome suggestions.

For a book

• List the reference alphabetically by the author’s surname.

• Use initials for the author’s other names.

• Follow this with the date of publication in brackets.

• Put the title of the book in italics (if typed) or underline the title ifhandwritten.

• List the publisher.

• Give the pages that were useful.

Example

Brown, A and Smith, A (1985): Apples. Heinemann Ed Aust.pp 224–250.

Internet sites

• As these are constantly changing you should give as muchinformation as you can.

• Give the web address, the author and the date accessedwhere possible.

Example

Burbank, H. (accessed May 2001): ‘Environmental Resource Room’http://www3.umassd.edu/Public/Exhibit/DES300/currmat2.html

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Scientific Journals

• Author’s surname and initials.

• The date of publication in brackets.

• Name of the article.

• Name of the journal underlined.

• The volume and series of the journal.

• The page numbers.

Example

Brown, R.J (1997): Fish recruitment in seagrass beds of NSW. Aust FishBiology 52(1), 57–65.

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Exercises – Part 1

Exercises 1.1 to 1.4 Name: _________________________________

Exercise 1.1: The role of receptorsa) Identify the role of the receptors in detecting stimuli.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Explain the knee jerk reaction in response to striking the kneecap.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

c) Look at the diagram below. It has the reactions that occur as youreye sees a bright light.

bright light sensory cellsin eyes

nerve muscle

musclecontracts

Describe the process shown in the diagram.

_____________________________________________________

_____________________________________________________

_____________________________________________________

32 Communication

Exercise 1.2: Senses in communication

Fill in the table below where possible.

Sense Example of communication in animals

sight

hearing

touch

smell

taste

other

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Exercise 1.3: The human eye

Fill in the names for the structure of the eye using the following terms:conjunctiva, choroid, sclera, vitreous humour, fovea, ciliary body, corneapupil, retina, iris, lens, aqueous humour, optic nerve, blind spot.

retina

Complete this table.

Part of the eye Function

conjunctiva

cornea

sclera

choroid

retina

iris

34 Communication

lens

aqueous humour

vitreous humour

ciliary body

optic nerve

Exercise 1.4: The range of visiona) Identify the limited range of wavelengths of the electromagnetic

spectrum detected by human eyes.

______________________________________________________

______________________________________________________

______________________________________________________

b) Give an example of an animal that can detect electromagneticwavelengths outside the range of human perception. State the rangeof vision for your example.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

c) A pit viper can find its prey even in the darkness of a burrow.How does this organism detect its prey?

______________________________________________________

______________________________________________________

______________________________________________________

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d) List three parts of the electromagnetic spectrum that humans cannotdetect with their senses.

_____________________________________________________

_____________________________________________________

_____________________________________________________

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Communication

Part 2: Eye can see clearly


AMENDMENTS

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Part 2: Eye can see clearly 1

Contents

Introduction ............................................................................... 2

The nature of light ..................................................................... 3

Refraction .............................................................................................3

Bending light with your eyes................................................................6

Accommodation......................................................................... 7

Modeling accommodation....................................................................8

The refractive power of the lens .......................................................11

Visual impairment ................................................................... 14

Hyperopia ..........................................................................................14

Myopia ...............................................................................................15

Correcting technologies ....................................................................16

Cataracts ...........................................................................................18

Summary................................................................................. 21


Exercises – Part 2 ................................................................... 25

2 Communication

Introduction

The eye needs a clear image of both nearby and far away objects.This part of the module explains how the nature of light and the structureof the eye work together to enable you to see things clearly.


• identify the conditions under which refraction of light occurs

• identify the cornea, aqueous humor, lens and vitreous humor asrefractive media

• identify accommodation as the focusing on objects at differentdistances, describe its achievement through the change in curvatureof the lens and explain its importance

• compare the change in the refractive power of the lens from rest tomaximum accommodation

• distinguish between myopia and hyperopia and outline howtechnologies can be used to correct these conditions.


• plan, choose equipment or resources and perform a first-handinvestigation to model the process of accommodation by passingrays of light through convex lenses of different focal lengths

• analyse information from secondary sources to describe changes inthe shape of the eye’s lens when focusing on near and far objects

• process and analyse information from secondary sources to describecataracts and the technology that can be used to prevent blindnessfrom cataracts and discuss the implications of this technologyfor society.

Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originallyissued 1999. Amended November 2002. The most up-to-date version can befound on the Board’s website athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html

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The nature of light

The fact that light bends when passing between clear media likewater, glass or plastic has shaped the evolution of the eye into thecomplex structure you see today. Light usually travels in straight lines.The process whereby light bends when it enters a different transparentmedium is called refraction.

This section will help you identify the conditions under which refractionof light occurs.

RefractionRefraction is the phenomenon where light appears to bend as the lightrays pass from one medium to another. You have seen the bending effectwhen you put a straight stick into clear water such as a fish tank.This apparent bending effect is shown below. In this case, you are seeingthe refraction of light rays.

observer

water

surface

apparent bend

apparent positionof stick

Diagram showing the image of a stick in water showing refraction.

When spearing a fish an experienced hunter would throw the spear belowwhere the fish appears to be swimming to hit the fish.

4 Communication

The scientific understanding of refraction is based on the following facts.

• As light travels through a given medium, it travels in a straight line.

• When light passes from one kind of medium into a second mediumwith a different optical density, the light path bends. This isrefraction.

• The refraction occurs only at the boundary. Once the light hascrossed the boundary between the two media, it continues to travel ina straight line; only now, the direction of that line is different than itwas in the former medium.

normal

The diagram shows refraction or bending of a beam of light as it passes intomaterial of different density.

Try this demonstration of refraction.

Take a ceramic bowl, a coin and a glass of water. Place the coin in thebottom of the bowl and move your head so that you are viewing the bowl atsuch an angle that you can just no longer see the coin.

See the diagram following.

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bowl

coin

angle ofview

angle ofview

Now add more water to the bowl.

What did you observe to happen as you poured more water into the bowl?

_________________________________________________________

Explain your observations using your knowledge of refraction.

_________________________________________________________

_________________________________________________________

Check your answer.

The whole shape of your eye is designed to make use of refraction inorder to see more clearly.

6 Communication

Bending light with your eyes

In Part 1 of this module you looked at the structure of the eye.Which parts are made up of a transparent (clear) medium? You mayremember that the parts called the aqueous and the vitreous humour arein fact very clear and the cornea is often called the window to the eye.The lens is also a transparent medium. Each of these parts has a differentdensity therefore as light passes through them they will refract orbend light.

The four refractive media found in the eye are:

• cornea

• aqueous humour

• lens

• vitreous humour.

The result of this refraction is that as light travels through these structuresit bends or refracts in such a way as to focus the light on the retina.Have a good look at the diagram below. Notice the way light bends sothat it is focused on the retina. The greatest amount of bending occurs atthe cornea-air surface.

cornea

vitreous humour

lens

aqueous humour

The cornea, aqueous humour, lens and vitreous humour are all refractive mediafound in the eye.


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Accommodation

To enable objects at different distances to be viewed clearly, your eyeshave evolved a method of focusing the image on your retina no matterwhere the image is located.

The ability of your eyes to change focus so that objects can be seensharply at varying distances is called accommodation. When the lens ofyour eye alters to make an image clear and focused, the eye is said to beaccommodated. Try this simple activity with your eyes.

• Hold your finger up in front of you and look at it so that the finger is infocus. Depending on your eyesight this could be as close as 25–30 cm.

• While keeping your finger in focus, observe the objects behind andfurther away from your finger. Write down what you notice aboutthe clarity of these objects.

_____________________________________________________

• Now focus your vision on a far object while keeping your finger inexactly the same position. Describe the clarity of your finger whilefocusing on the background.

_____________________________________________________

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When focusing on the near object thedistant object is blurred.

When focusing on the distant objectthe near object is blurred.

Your eyes can change focus but cannot have everything in focus at thesame time.

Types of lenses

The lens found within the eye is a convex lens. It bulges out in the centre.An other type of lens is a concave lens. This type of lens goes in atthe center.

Convex lens Concave lens

Modeling accommodation

A good way to model accommodation is to pass parallel rays of lightthrough some convex lenses. A convex lens converges (brings together)light into a focal point. The distance from the lens to the focal point iscalled the focal length. The curvature of the lens is responsible forthe focal length. The greater curvature of the lens the shorter thefocal length.

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parallel light

F'

convex lens

focal length

If you have several convex lenses you could shine light through them andrecord the focal length for each lens.

Different curvature of a convex lens

In this activity you will measure the focal length of two convex lenses.The focal length is the distance from the middle of the lens to the pointwhere the light rays converge. Mark on the diagrams the focal point of eachlens. Now use the grid squares (1 cm) to estimate the focal length of eachlens below by counting the squares from the middle of the lens to thefocal point.

Convex lens 1

Convex lens 2

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Feature Lens 1 Lens 2

Focal length

Curvature of lens

From the two lenses above what is the relationship between the curvatureof the lens and the focal length?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answers.

On the LMP Science Online webpage there are instructions on how to use alight box to examine the behaviour of lenses. You can do the above exerciseonline in colour if you prefer at: http://www.lmpc.edu.au/science

If you don’t have access to convex lenses then you can modelaccommodation in the eye by using drops of water of different thicknessin the activity below.

In this activity you will need a firm sheet of clear plastic such as a CD coveror a piece of glass like a microscope slide. You will also need access towater drops.

Procedure

• Place a drop of water on your sheet of plastic or piece of glass.

drop of water clear plastic or glass

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Notice how you can make a thin drop or a fat drop.

• Start with a fat drop and hold it over some printing such as anewspaper.

• Move the drop up and down to see the distance required to focus thewriting on a sheet of newspaper.

print media

Now make a thin drop and note the different distance required to focusthe print.

thin drop of water clear plastic or glass

The fat and the thin drop of water models the changing shape of the eye’slens. They are examples of convex lenses. The fatter drop should havehad a shorter focal length than the thin drop of water.

The lens is responsible for fine focusing the image onto the retina whilethe cornea is responsible for most of the refraction of light in the eye.Likewise the lens of the eye assumes a large curvature (short focallength) to bring nearby objects into focus and a flatter shape (long focallength) to bring a distant object into focus.

The refractive power of the lens

The importance of accommodation is the ability of the eye to change theshape of the lens and focus on objects whether they are near or far.This is achieved by the contraction of the ciliary muscles in theciliary body.

12 Communication

Maximum accommodation

When the ciliary muscles contract the suspensory ligaments, that hold thelens are released and the lens becomes more rounded. This is fullyaccommodated and maximum refraction of light. Near objects would bein focus.

At rest

When the ciliary muscles relax the suspensory ligaments are taut and thelens is flattened. Vision would be focused on far objects and therefractory power would be at a minimum.

Distance focused eye:• ciliary muscles relaxed• suspensory ligaments tight• lens is flattened• minimum accommodation

Close focused eye:• ciliary muscles contracted• suspensory ligaments loosened• lens is rounded• maximum accommodation

Process and analyse information form secondary sources to describe changesin the shape of the eye’s lens when focusing on near and far objects.

Hint

A good way of processing information on the changes in the shape of eye’slens during accommodation is to draw a diagram like the one above.The diagram should show the contraction and the relaxation of the ciliarymuscles and the suspensory ligaments. It should also illustrate the change inshape of the lens through these actions.

On the LMP Science Online web site there is an animation that showsaccommodation and the change in the shape of the lens. If you have accessto the Internet visit the site and have a look at the animation. Use this as asecondary source of information. Analyse the animation by writing adescription of the changes that occur as the object gets closer to the lens.

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Drawing of the shape the eye’s lens when focusing on close ordistant objects.

Distance focused eye Close focused eye

Write your description of accommodation in the space below.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Do Exercise 2.2.

14 Communication

Visual impairment

You have just learnt that to focus on nearby objects requires a differentlens shape to that required for focusing on distant objects. People withclear vision have eyes where the lens adjusts correctly in all situations.For people who can’t see clearly in some situations the problem is causedby their eye’s inability to focus light directly on the retina.

Glasses (or contact lenses) are used to change the way light is refractedso objects appear in focus. People who wear glasses have a problem withseeing things clearly either close up or far away.

In this section you are required to distinguish between the two mainkinds of eye focusing conditions, namely myopia and hyperopia.You might even have one of these conditions yourself - they arecommonly known as short-sightedness and far-sightedness.

Cataract, a clouding of the lens causing blurred vision, is another type ofvisual impairment. The technology used to prevent blindness fromcataracts is also detailed and you will be required to discuss theimplications of this technology for society.

Hyperopia

Far-sightedness is the inability of the eye to focus on objects that areclose. The proper term for this is hyperopia. The far-sighted eye has nodifficulty viewing distant objects. There is a problem however, whenpeople with hyperopia view objects close to the eye.

The lens of the far-sighted eye can no longer assume the very roundedshape required when viewing nearby objects. This causes these imagesto be focused at a location behind the retina meaning the light-detectingcells will perceive a blurred image. The problem is most common duringlater stages in life because of the weakening of the ciliary muscles andthe decreased flexibility of the lens.

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light is focused behind the retina

In hyperopia a close object produces a blurred image because the lens cannotproduce the rounded shape necessary to bend light sufficiently to focus theimage on the retina.

Myopia

Short-sightedness or myopia is the inability of the eye to focus on distantobjects. The short-sighted eye has no difficulty viewing nearby objectsyet the ability to view distant objects is a problem. This is because thelight from distant objects is bent or refracted more than is necessary.The problem is most common as a youth, and is usually the result of abulging cornea or an elongated eyeball.

light is focused in front of the retina

A short-sighted person viewing a distant object focuses the image in front ofthe retina.

If the cornea bulges more than its customary curvature, then it tends torefract light more than usual. The images of distant objects are focusedin front of the retina. If the eyeball is elongated in the horizontaldirection, then the retina is placed at a further distance from thecornea-lens system; subsequently the images of distant objects form infront of the retina. On the retinal surface, where the light-detecting cellsare located, the image is not focused. The nerve cells thus detect ablurred image of distant objects.

16 Communication

Correcting technologies

Eyeglasses or spectacles and contact lenses are the most common way tocorrect these conditions.

Correcting hyperopia

In order to correct the far-sighted eye, some devise must be used torefract the light. Since the lens can no longer change to the highlycurved shape required to view nearby objects, it needs some help.The far-sighted eye is assisted by the use of a convex lens that willconverge the light rays further.

A convex lens converges light rays and corrects the problem of hyperopia.

This converging lens will refract light before it enters the eye andtherefore enable the eye to focus light onto the retinal surface. This isexplained in the diagram below.

lens converges the image

A convex lens corrects the problem of hyperopia by focusing the imageonto the retina.

Correcting myopia

The nature of the problem of nearsightedness is that the light is focusedin front of the retina. Light can be refracted artificially using a lenswhich diverges the light rays just enough so that it focuses on the retina.

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Hence the cure for the nearsighted eye is to equip it with a diverging lenscalled a concave lens. See the diagram below.

lens converges the image

A concave lens corrects the problem of myopia. Note that the lens is stillcurved outwards at the front but has a much deeper curvature at the back.

A concave lens diverges light rays.

A diverging lens acts on the light rays before it reaches the eye.This light will be converged by the cornea and lens producing a focusedimage on the retina.

There are also more permanent methods for correcting sight problems.

Surgical modification of the cornea

Refractive laser surgery can be used to change the shape of the corneapermanently so that it converges or diverges the light enough to correctthe condition. During this surgery a flap of the cornea is cut and liftedand a laser beam is used to reshape the rest of the cornea, the flap oftissue is then replaced.

The original corrective eye surgery was known as radial keratotomy orthe ‘Russian Operation’ because of its inventor. Recent advances in lasersurgery have changed the technique. An ultraviolet-argon laser breaksintermolecular bonds and thin layers are removed from the cornea

18 Communication

reshaping the curvature of the cornea. The process is computer-controlled for greater accuracy.

Do Exercise 2.3.

Cataracts

The lens of the eye is made up mostly of water and protein. The proteinis arranged to allow light to pass freely. Sometimes the protein clumpstogether clouding small areas of the lens. This obstructs light fromreaching the retina causing vision problems and is called a cataract.

A cataract is a progressive clouding of the lens and happens over aprolonged period of time. The amount of visual impairment depends onhow much clouding of the lens occurs. The degree of cataract formationdepends on factors such as age, lifestyle or diseases like diabetes.

The technology used to prevent blindnessfrom cataracts

The technology used to prevent blindness from cataracts is thereplacement of the cloudy lens with an artificial intraocular lens (IOL).

There are three methods of cataract surgery:

• phacoemulsification

• extracapsular extraction

• intracapsular extraction.

Phacoemulsification is the most common technique. A small incision ismade where the cornea meets the sclera. A probe is inserted that emitshigh frequency vibration that breaks the lens into pieces. The lens is thensuctioned out and replaced with an intraocular lens. The incision is sosmall that usually stitches are not required. The operation is verysuccessful and millions of these operations take place each year.

The other methods are used when the lens does not break up easily.

Fred Hollows Foundation

The social implication of the technology of cataract treatment can beseen in the work of the Fred Hollows Foundation. Cataract blindness is

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found all around the world. It is estimated that 20 million people indeveloping countries are suffering blindness caused by cataracts.An older person who develops cataracts in a developing country usuallyonly lives for a few years after blindness sets in. By returning sight tothese people their lives are prolonged and the quality of their existence isgreatly improved.

The operation needed to cure cataract blindness is simple and only takesabout fifteen minutes. People in developing countries cannot afford theoperation without assistance. Fred Hollows trained local doctors incountries such as Nepal, Vietnam and Eritrea to replace the clouded lensof cataract sufferers with an artificial lens. Since his death his foundationhas set up factories to produce cheap affordable lenses. During hislifetime Fred Hollows helped a quarter of million people to see again andthe work is continued by his foundation.

Process information from secondary sources to describe cataracts and thetechnology that can be used to prevent blindness from cataracts and useavailable evidence to discuss the implications of this technology for society.

There are some useful sites to be found on the Internet. Use a search engineand search for secondary information using terms such as ‘cataracts’ and‘cataract surgery’. For the social implications of the technology search forinformation using search words like ‘Fred Hollows foundation’.

There are also some useful sites gathered for you on the LMP ScienceOnline webpage that can be accessed at: http://www.lmpc.edu.au/science

If you do not have Internet access then library books or a letter written to theFred Hollows Foundation would be a good source of secondary information.

Process the information that you gather by answering thefollowing questions.

1 What are cataracts?

2 How do they form?

3 What technology can be used to prevent blindness?

4 How would you search for secondary information to describecataracts and the technology used to prevent blindness?

Do Exercise 2.4 to complete this part of the module.

20 Communication

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Summary

During this part of the module you should have carried out the followingfirst-hand investigations and tasks using secondary information.

First hand investigations

Make sure you can describe how you did the following first-handinvestigation. List the precautions that need to be taken during theexperiments and the safe working practices you used.

• Plan choose equipment or resources and perform a first-handinvestigation to model the process of accommodation by passingrays of light through convex lenses of different focal lengths.

Secondary information• Process and analyse information from secondary sources to describe

changes in the shape of the eye’s lens when focusing on near andfar objects.

• Process and analyse information from secondary sources to describecataracts and the technology that can be used to prevent blindnessfrom cataracts and use available evidence to discuss the implicationsof this technology for society.

Summary of content• Refraction is the bending of light as it moves into a

different medium.

• The cornea, aqueous humour, lens and vitreous humour arerefractive media found in the eye.

• The result of the properties of light is the image focused on the retinais upside down, back to front and much smaller than the originalimage. The brain is able to interpret this information and you see theworld the right way up.

22 Communication

• Accommodation is the ability to focus objects at different distancesthrough a change in the curvature of the lens by the contraction ofthe ciliary muscles.

• The lens at rest focuses on distance objects, the ciliary muscles arerelaxed, the suspensory ligaments are taut, the refractive power is ata minimum and the lens is flatter. At maximum accommodation thelens is rounded, the refractory power is at its greatest, the ciliarymuscles are contracted and the suspensory ligaments are loose.

• Myopia is short-sightedness, the image of far objects is blurredbecause the refractory power of the lens is too great and the image isfocused in front of the retina.

• Hyperopia is far-sightedness, close objects are blurred because theimage is focused behind the retina.

• The technologies that are used to correct these conditions are lensessuch as glasses and contact lenses and refractive eye surgery tochange the shape and refractory power of the cornea. A concavelens is used for myopia and a convex lens for hyperopia.

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Suggested answers

Refraction

As you add more water the coin becomes visible.

More water has increased the angle of refraction.

Accommodation

When your finger is in focus the objects behind are blurred.

In the second case the image of the finger is blurred while thebackground is in focus.

The curvature of a convex lens

Feature Lens 1 Lens 2

Focal length (cm) 4.5 7.3

Curvature of lens more curved less curved

The relationship between the curvature of the lens and the focal length isthat the greater the curvature the less the focal length.

24 Communication

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Exercises - Part 2

Exercises 2.1 to 2.4. Name: _________________________________

Exercise 2.1: Refractiona) What is refraction?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Under what conditions does refraction occur?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

c) Name the refractive media found in the eye.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

26 Communication

d) On the diagram following label the cornea, aqueous humour, lensand vitreous humour and mark with a cross the four points whererefraction occurs.

Exercise 2.2: Accommodationa) What is accommodation in the eye?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

b) How does the eye change the focus from distant to near objects?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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c) Use the following words to fill in the blanks below.

minimum ciliary relaxed rounded distances focus contracted

Accommodation is the ability to __________ objects at different

____________ through a change in the curvature of the lens by the

contraction of the_____________________muscles.

The lens at rest focuses on distance objects, the ciliary muscles

are________________, the suspensory ligaments are taut, the

refractive power is at a ____________ and the lens is flatter. At

maximum accommodation the lens is _____________, the refractory

power is at its greatest, the ciliary muscles are ____________ and the

suspensory ligaments are loose.

d) Describe the change in the shape of the lens when focusing on nearand far objects.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

28 Communication

d) Look at the diagrams below and circle the eye that is focused on anear object. Give three reasons for your answer.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Exercise 2.3: Visual impairmenta) Distinguish between myopia and hyperopia.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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b) What sort of lens is required to help a person with myopia?

_____________________________________________________

_____________________________________________________

c) What sort of lens would help a person with hyperopia?

_____________________________________________________

_____________________________________________________

d) Describe the surgical techniques used on the cornea to correctmyopia or hyperopia.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Exercise 2.4: Cataracta) Discuss the social implications of the technology available to

treat cataracts.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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Communication

Part 3: I can see the light


AMENDMENTS

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Part 3: I can see the light 1

Contents

Introduction ............................................................................... 2

Photopigments .......................................................................... 4

Photoreceptor cells ..............................................................................5

Nature of photoreceptor cells .............................................................8

The role of rhodopsins in rods ...........................................................10

Colour vision ........................................................................... 12

Seeing colour......................................................................................12

Colour blindness ................................................................................13

Colour communication ......................................................................14

Depth perception ................................................................................17

Summary................................................................................. 21


Exercises – Part 3 ................................................................... 25

2 Communication

Introduction

Vision involves the transfer of light energy into electro chemical signalswithin the nervous system. These signals or nervous impulses are thelanguage of the brain and they construct our perception of thevisual world.

Light energy stimulates light sensitive pigments on the retina andelectro chemical signals are carried by nerve fibres to the brain viathe optic nerve.

Photoreceptors in the retina are located in specialised cells called rodsand cones. Both of these cells contain photopigments. Any defect in oneor more of the cone cells will affect colour sensation and causes colourblindness. Colour blindness results from the lack of one or more of thecolour sensitive pigments. Colour and its perception play a big role incommunication among many different kinds of animals.


• identify photoreceptor cells as those containing light sensitivepigments and explain that these cells convert light images intoelectro chemical signals that the brain can interpret

• describe the differences in distribution, structure and function of thephotoreceptor cells in the human eye

• outline the role of rhodopsins in rods

• identify that there are three types of cones, each containing aseparate pigment sensitive to either blue, red or green light

• explain that colour blindness in humans results from the lack of oneor more of the colour-sensitive pigments in the cones

• explain how the production of two different images of a view canresult in depth perception.

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• process and analyse information from secondary sources to compareand describe the nature of photoreceptor cells in mammals, insectsand in one other animal

• process and analyse information from secondary sources to describeand analyse the use of colour for communication in animals andrelate this to the occurrence of colour vision in animals.

Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originallyissued 1999. Amended November 2002. The most up-to-date version can befound on the Board's website athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html

4 Communication

Photopigments

Until the 17th century it was thought the cornea was responsible for thedetection of light. In 1604, the famous astronomer Johannes Keplerexplained in detail how vision works. He said light enters the eye then isrefracted and focused through the lens onto the retina. Kepler identifiedthe retina as the light sensitive receptor of the eye.

The retina is a thin sheet of cells (0.5 mm thick) that containsphotoreceptor cells. These cells are called rods and cones. They are atype of modified neurone (nerve cell).

When a vertical section of the retina is examined under a microscope itis obvious that the retina is a complex structure of many neuronespacked together and contains a number of different nerve cell types.Ganglion cells (the neurones of the retina taking the message away to thebrain) lie closest to the lens and front of the eye. These are connectedto the bipolar cells which then connect to the photoreceptor cells.The photoreceptor cells (consisting of rod and cone cells) lie outermostin the retina against the pigmented epithelium and choroid.

Light must, therefore, travel through the thickness of the retina beforestriking and activating the rod and cone cells. Here the light energy isconverted into electro-chemical signals consisting of a stream of sodiumand potassium ions that move across the cell membrane of the neurone.More about this will be discussed in Part 6 of this module. The opticnerve contains the ganglion cell axons running to the brain where theinterpretation of the light image is made.

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epithelium cells

rod cells

cone cells

bipolar cells

ganglion cells

optic nerve fibre

light rays

back of the eye

front of the eye

optic nerve

The structure of the retina. Note the direction of the light. Light must passthrough the ganglion and bipolar cells before reaching the light sensitive rodand cone cells. The electro-chemical signal is sent back through the bipolarand ganglion cells and on to the optic nerve.

Photoreceptor cells

Photoreceptor cells are responsible for an animal’s perception of vision.They contain light sensitive pigments that absorb light energy. When thepigments absorb light they convert the information into an electrochemical signal that the brain can interpret.

There are two types of light sensitive receptors in the retina of thehuman eye.

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∑ Rods are responsible for night vision, and are located in theperipheral retina.

∑ Cones are responsible for colour vision and fine detail.They function best under daylight conditions and are mostlyconcentrated in a region of the retina called the fovea.

Structure of rods and cones

The diagram below shows the structure of rods and cones. They arenamed after their shape. Rod cells are longer and thinner than cone cellsand have a photopigment called rhodopsin. They contain plate-likemembranes containing light-sensitive pigments at one end and aconnection to nerve cells on the other end. Cone cells have a pointed(cone-shaped) end that contains photopigments called photopsinsarranged in plate-like membranes.

membranes containingpigments

nucleus

rod cell cone cell

mitochodria

Structure of rods and cones

Distribution of rods and cones

The photoreceptors are unevenly distributed over the retina. Cones areconcentrated at the fovea, the area of best vision and highest acuity.

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retinafovea

blind spot

optic nerve

retina

The fovea contains the highest concentration of cone cells. While the rod cellsare scattered over the rest of the retina.

Rods are not present in the fovea and are more concentrated at the sidesof the retina. There are 120 million rods and 6.5 million cones.

Den

sity

(th

ousa

nds

per

squa

re m

m)

–80 –60 –40 –20 0 20 40 60 80

200

150

100

50

0

Angular distance from fovea (degrees)fovea

rod density rod density

cone density

The distribution of rod and cone cells across the retina. Note how the numberof cones per square mm drops off rapidly away form the fovea. The rods arenot found at the fovea and also have a decreasing density away formthe fovea.

Function of rods and cones

Rod cells are important in night vision and peripheral (or side) vision.They are very efficient photoreceptors and respond to low levels of light.They detect movement and shapes but do not distinguish betweencolours. There are more rods than cones and they are more sensitive tolight than the cones. The photosensitive pigment in rods is a form ofrhodopsin that is particularly sensitive to blue-green light (505 nm).

Cones cells are only stimulated by bright light and are important in dayvision, colour vision and acuity of vision. The number of cone cells inan area decides the visual acuity that is possible. When you are lookingat fine print you position your head so that the image falls directly on the

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fovea where most of the cone cells are located. At night it is better tolook out of the side of your eye if you want to see something in dim light.This forces the image to fall onto an area that has rod cells which aremore sensitive to low light.

Birds such as hawks and eagles have two area of visual acuity (fovea)and four types of cone cells.

Do Exercise 3.1.

Nature of photoreceptor cells

Seeing has great survival value resulting in the evolution of a variety oflight sensitive cells among animal species. One of the amazing factsabout vision is that rhodopsin is used in all visual systems whether theorganisms are a flatworm or a human.

Simple eyes

Simple eyes (called ocelli) are found in worms (such as the flatworm),molluscs and crustaceans. Planaria, a type of flatworm, have eyes thatare located in a hollow called a cup eye. These eyes do not detect colourand only give information on the direction of the light source.They interpret light signals and turn their bodies so that the minimalamount of light is falling on their eyes and then swim in that directionaway from the light.

light

photoreceptor cell

pigment cup

nerve fibres

Simple eyes only give directional information. No image is formed.(Photo: David Stanley)

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Compound eyes

Insects have compound eyes made up of a large number of separate lightreceptors called ommatidia. They have three-colour vision includingthe ultraviolet range of the spectrum. The eye forms an image.Each ommatidium has its own cornea and a lens made up of a crystallinecone. The number of ommatidia varies from only 20 in some crustaceansto the dragonfly which has more than 28 000. These eyes can have highflicker speeds for detecting movement; can detect ultraviolet light and thepolarisation of light.

lens crystalline cone

retinal cell nerve fibresto brain

Compound eye of a fly. (Photo: David Stanley)

Single lens eye

Mammals have a more complex camera type of eye found in allvertebrates and cephalopods. These eyes can focus and form an image.There are different types of receptors found in the eye. Some are capableof colour vision while others are important in visual acuity and nightvision. By having two eyes information can be gathered about depthperception. Each eye has a single lens.

The mammal eye is a single lens eye that produces a colour image althoughthat colour image may not be seen exactly as humans see it.(Photo: Jane West © LMP)

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In the following activity you will compare and describe the nature ofphotoreceptor cells in the eyes of a mammal, the compound eye of an insectand in the simple light receptors of a flatworm.

Hint

The information above is a good starting point. You could also look forinformation by searching the Internet using search words like ‘animalvision’. There are also some webpages gathered for you on the LMPScience Online web site at: http://www.lmpc.edu.au/science

Biology textbooks and popular scientific journals such as New Scientist arealso good secondary sources of information.

A good way to process the information is to summarise the information in atable. You could use the format given below. When analysing informationyou can look for similarities or generalisations that are common to all visualsystems and look for differences such as whether they have colour vision orform an image.

Group Examples Nature of photoreceptorcells

Vision

flatworm planaria rhodopsin located in simplecup eyes

direction of light

insect bee rhodopsin located incompound eyes thatconsist of individualommatidia

colour vision, depthperception,detection ofmovement

mammal dog, human, cat rhodopsin, rod and conecells

depth perception,colour vision,detection ofmovement, nightvision

The role of rhodopsin in rods

Rhodopsin is a photosensitive pigment. It consists of two moleculesjoined together, they are retinal (a derivative of vitamin A) and opsin.When light falls on rhodopsin a series of chemical reactions break themolecule of rhodopsin into retinal and opsin. This generates theelectrical impulse that is transmitted to the bipolar cells, the ganglioncells and then through the optic nerve where the signal is interpreted by

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the brain. Several milliseconds are required before the absorption oflight can be recorded as electrical activity in the receptor cell membrane.Opsin and retinal then recombine to form rhodopsin and can then besplit again by light. The reaction is reversible and is known as thevisual cycle.

Rods cells only have a form of rhodopsin often called visual purple.It responds to light in the blue–green area of the spectrum.

Rel

ativ

e ab

sorb

ance

400 450 500 550 600 650 700

rod 498 nm

Wavelength (nm)

Absorption spectrum for rhodopsin

Cones have three types of photopigments and will be dealt with in thenext part on colour vision.

Do exercise 3.2

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Colour vision

In 1802 the scientist and medical doctor Thomas Young concluded thatthe retina responded to only three principle colours which combined toform all the other colours in humans. These three colours of light arered, blue and green.

It is the cone cells that are the photoreceptors responsible for colourvision. It is now known that cone cells contain three different kinds ofphotopigments each sensitive to a different set of colour wavelengths.Each photopigment has its own form of opsin combined with retinal toform pigments known as photopsins. These three differentphotopigments combine to produce the array of different hues detectedby the human eye.

Seeing colour

There are three types of cone cells:

• red cones

• blue cones

• green cones.

Each type of cone has a different range of light sensitivity but theirsensitivities overlap. When light energy hits the eye, more than one ofthe three types of cone cells will be stimulated. The retina and the brainprocess the mixture of the stimulation so that different hues andintensities are perceived, allowing many more colours to be recognisedthan the three detected by the cone cells.

The first type of cone cell is called S cones (S for short wavelength437 nm) or blue cones. These are sensitive to blue and violet light.Next is the M or green cones (medium wavelength 533 nm) theserespond to green light. The third type is L cone or red cones (longwavelength 564 nm) these respond to the red end of the spectrum.

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The graph below shows the sensitivity of each type of cone cell.Notice that they do overlap.

Abs

orba

nce

(%)

100

0350 400 450 500 550 600 650 700 750

blue cones437 nm green cones

537 nm red cones564 nm

Wavelength (nm)

Colour discrimination occurs through the integration of informationarriving from all three types of cones. For example, the perception ofyellow results from a combination of inputs from green and red cones,and relatively little input from blue cones. If all three cones arestimulated, white is perceived. If a red light is shone into the eyes thenonly the red cones will fire and the colour is perceived as red. If none ofthe cones fire the colour is perceived as black.

Do Exercise 3.3.

Colour blindness

Full colour vision depends on having all three types of cone cells beingpresent and functioning properly. Any defect in one or more of thesecone cells will affect colour sensation and people with this condition areknown as colour blind. The most common form of colour blindness isred/green colour blindness. People with this condition have troubletelling the difference between brown, red and green.

Colour blindness is the inability to distinguish certain colours. It occurswhen one or more of the cone types are missing or defective to anyextent. They may be absent entirely or unable to manufacture thenecessary signals to the brain.

Colour blind people may experience no colour sensation or abnormalcolour matching and colour confusions. Colours that look different to

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people with normal colour vision, can look the same to people withdefective colour vision. Grass may appear green to non-colour blindpeople, but be the same colour as orange for people with certain colourdefective vision. There is also a reduction in the number of separatecolours that can be distinguished in the spectrum.

Test your own colour vision by looking up the links for this module in theLMP Science Online web site at: http://www.lmpc.edu.au/science


Colour communication

Animals that use colour to communicate include fish, amphibians,reptiles and birds. Humans and some other primates are among the fewmammals that see colour as you see it.

Animals use colour communication for a variety of reasons including:

• to signal their availability to mate and other kinds of reproductivebehaviour like courtship

• to warn off predators

• protective coloration and camouflage.

If an animal is using colour for communication, to be effective thereceiver must be capable of colour vision. Examples of colourcommunication are:

• camouflage

• mimicry

• sexual dimorphism

• breeding colours

• warning colours.

Camouflage

Camouflage is hiding by blending into the environment. Some animalsare masters of this and can change the colour of their skin to matchwherever they are. Examples of animals that can do this are chameleonsand the octopus.

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Two chameleons on a stick. The lower one has been there for a while and haschanged colour to match the surroundings. The top chameleon has justarrived. (Photo: Jane West © LMP)

Mimicry

Many animals that are poisonous advertise this by having strikingcolouration. Other animals who are not poisonous have evolved thesame colouration to fool predators into not attacking them. An exampleof this is the Monarch butterfly and the Viceroy butterfly. Both havesimilar appearance but only the Monarch has a bad taste.

Sexual dimorphism

Sexual dimorphism is different appearance between the sexes. In manyspecies the males and females can be distinguished by their differentcolours or sizes.

The example below shows a male lion. Only the male lion developsthe mane.

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The male lion is sexually dimorphic from the female.(Photo: Jane West © LMP)

Birds also show dramatic sexual dimorphism. Often the male bird isbrightly coloured while the female is plain coloured.

Warning colours

Some animals change colour to give a warning that they are about toattack. The blue-ringed octopus is a famous example of this. The smalloctopus uses camouflage to hide in rocks but when threatened smalliridescent blue rings appear all over the surface of the skin.

Breeding colours

Many birds take on different colours during the breeding season.The example below is a male puffin. During the breeding season thebands on the beak are bright, while outside of the breeding season thebands fade.

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Male puffin with breeding colours on its beak.(Photo: Upgrade Business Systems Pty Ltd)

Animals that use colour for communication must be able to send themessage to another organism that can receive the message. This gives a cluethat the species sees in colour. If you look at the examples above you willsee that they are all groups of animals that have colour vision (birds, reptiles,primates). Find three examples of colour communication in animals andthen relate this communication to colour vision.

There are some useful web sites gathered for you on the LMP ScienceOnline web site at: http://www.lmpc.edu.au/science

Do Exercise 3.5 to record your answers.

Depth perception

The ability to see depth in our three dimensional world is calledbinocular vision or sometimes referred to as stereoscopic vision.Depth perception results from having forward facing eyes.This produces an overlap between the view from the left and the viewfrom the right eye. The images formed by both eyes are sorted in thebrain so that a three dimensional picture is formed.

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extent of side vision

angle of field of view

area of depth perception

Depth perception is achieved by having a field of view overlap.

Activity Field of view overlap

Put a hand over your left eye and note how far to the left your right eye cansee. Then repeat this time using the right eye. See how far to the right yourleft eye can see. There is a large overlap between the two fields.

The slightly different angles between the views from each eye givesdepth perception.

Lemur Human

Field of view overlap in a lemur and a human.

You can make assumptions about the ability of other animals to see depthby studying the arrangement of their eyes. Animals that have forwardfacing eyes are probably able to see depth and the need to judge distanceis important for their survival. Predators have forward facing eyes whilemany mammals such as horses and antelopes have eyes on the side oftheir heads. This is good for keeping an eye out for predators but,because the field of view overlap is limited, there is less depthperception. Horses and cows have a field of view of 350 degrees but only65 degrees of that is overlap for depth perception.

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monocular visionmonocular vision

binocular vision

Field of view overlap in a herbivore

Humans have the eyes of a predator. Animals that do not have anoverlap of vision have monocular vision. Rock doves can see300 degrees but only 30 degrees of binocular vision.

Animals like monkeys that jump from tree branch to tree branch need avery sharp sense of depth perception. Birds of prey would also needexcellent stereoscopic vision to swoop down on their prey at high speeds.

Peregrine falcon has excellent depth perception provided by the forward facingeyes. (Photo: Jane West © LMP)

20 Communication

The table below shows a list of animals with forward facing eyes. Complete thetable by describing how their perception of depth helps them survive intheir environment.

Animal Survival value

Gorilla

Cat

Koala

Owl

(Photo: Jane West © LMP)

Check your answers.

Do Exercise 3.6 to complete this part of the module.

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Summary

During this part of the module you should have carried out thefollowing tasks using secondary information. There were no first-handinvestigations.

Secondary information• Process and analyse information from secondary sources to compare

and describe the nature of photoreceptor cells in mammals, insectsand one other animal.

• Process and analyse information from secondary sources to describeand analyse the use of colour for communication in animals.

Summary of content• The retina is a thin sheet of cells that contains the photoreceptors

rods and cones. These cells contain light sensitive photopigments.

• The cone cells are most profuse in the central area called the fovea,they have a cone shaped end and are important in visual acuity andcolour perception. There are three types of cone cells eachcontaining a different photopigment that is sensitive to either red,blue or green light.

• Rod cells are located away from the fovea, they have a rod shapedend and they are important in vision when the light conditionsare dim.

• There are four types of photopigments found in the human eye.Three are found in cone cells and each is sensitive to differentwavelength ranges of the visual spectrum. The fourth is found in rodcells and is sensitive to blue-green light.

• Colour blind people have a type of cone cell missing in their retinaso are unable to distinguish between some colours.

• Depth perception is dependent on a field of view overlap.

22 Communication

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Suggested answers

Depth perception

Animal Survival value

Monkey Forward facing eyes with great field of view overlap give good depthperception important when jumping from tree to tree.

Cat Predator eyes facing forward important when springing onto prey whenhunting.

Koala Forward facing eyes with great field of view overlap allows the koala to movebetween branches.

Owl Good depth perception for swooping down onto prey.

24 Communication

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Exercises - Part 3


Exercise 3.1: Photoreceptor cellsa) Name the two types of photoreceptors found in the human eye.

_____________________________________________________

_____________________________________________________

b) Fill in the table

Features Rod cells Cone cells

Draw thestructure

Distribution

Function

26 Communication

Exercise 3.2: Photoreceptor cells continueda) What are some of the differences in visual perception between a

simple cup eye in a flatworm, the compound eye of an insect and thecamera type of eye found in mammals?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

b) Outline the role of rhodopsin in rod cells.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Exercise 3.3: Seeing coloura) Describe the difference in sensitivity of the three kinds of

photopigments found in cone cells.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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Exercise 3.4: Colour blindness

From the syllabus you are asked to:

explain that colour blindness in humans results from the lack of one ormore of the colour-sensitive pigments in the cones.

The verb explain has a specific meaning in the context of the Biologysyllabus. This meaning is:

relate cause and effect; make the relationship between things evident;provide why and/or how.

The scaffold following sets out to show how to approach a question thatuses the verb explain.

Question

Explain that colour blindness in humans results from the lack of one ormore of the colour-sensitive pigments in the cones.

Method of answering

Step 1 Firstly you need to describe the relationship between colourblindness and the lack of one or more colour sensitive pigments inthe cones.

Step 2 To do that fill in the tables below showing the cause andeffect between colour blindness (the effect) and lack of one or morecolour-sensitive pigments in the cones (the cause).

Step 3 Next you have to describe why or how one is caused by the other.That is, why does the lack of a colour-sensitive pigment result in colourblindness?

Step 4 Now take your answer out of the boxes and write down the sameinformation in complete sentences.

28 Communication

Cause Effect

Why?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

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Exercise 3.5: Colour communicationa) Give three examples of animal communication using colour and then

relate this to the occurrence of colour vision.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Exercise 3.6: Depth perceptiona) How does the production of two images lead to depth perception?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

30 Communication

b) The mountain goat below has forward facing eyes. Most sheep haveeyes on the side of their heads for good peripheral vision. Whatpossible survival benefits would forward facing eyes be for themountain goat?

(Photo: Jane West © LMP)

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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Communication

Part 4: Making sounds


AMENDMENTS

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Part 4: Making sounds 1

Contents

Introduction ............................................................................... 2

Sound energy............................................................................ 3

Sound is a useful and versatile form of communication.....................4

Looking at sound....................................................................... 5

Vibrating objects...................................................................................5

Describing a wave................................................................................7

What’s the pitch?................................................................................10

Making sounds ........................................................................ 14

The human larynx...............................................................................14

Structures used for sound communication by other animals ...........15

Summary................................................................................. 17


Exercises – Part 4 ................................................................... 21

2 Communication

Introduction

Sound is a very important for communication in humans and otheranimals. Sound is a form of energy that requires a medium to betransmitted therefore sound cannot travel in a vacuum. For animalssound is a useful way of communicating and different structures haveevolved to create and to perceive sound. The human larynx is anexample of this.


• explain why sound is a useful and versatile form of communication

• explain that sound is produced by vibrating objects and that thefrequency of the sound is the same as the frequency of the vibrationof the source of the sound

• outline the structure of the human larynx and the associatedstructures that assist the production of sound.


• plan and perform a first-hand investigation to gather data to identifythe relationship between wavelength, frequency and pitch of a sound

• gather and process information from secondary sources to outlineand compare some of the structures used by animals other thanhumans to produce sound.


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Sound energy

If you go out into the bush or National Park and listen to all thesounds you will notice that most of them are animals calling each other.Whether they are calling for a mate, signaling danger or announcinga food source, sound is very important for communication amongmost animals. Some animals such as bats use sound to ‘see’their environment.

Animals living in water are very dependent on sound vibrations as wateris a very effective medium for carrying sound energy. Solids like rockstransmit sound waves well and animals living close to the ground likesnakes can detect vibrations.

Two snakes with most of their bodies in contact with the ground.(Photo: Jane West © LMP)

4 Communication

Sound is a useful and versatile formof communication

Sound is one of the most important forms of communication. If youlisten to birds singing there are different sounds to communicate a threat,willingness to mate and the location of food. Dogs have many differentsounds for communication. If you own a dog you will probably be ableto tell if there is someone coming to the door by the sound your dogmakes. If the dog is in pain it will let you know by whining.

This ability to communicate different messages reaches a peak in humanswhere speech is used to communicate a range of emotions and intentions.

Sound can also travel over vast distances. Howler monkeys can be heardthroughout the forest areas where they live and the song of Humpbackwhales is heard across oceans.

Sound may also be used to locate organisms. If the sound is loud theanimal is close so changing directions may find the source of the sound.

In summary sound is useful because:

• a variety of sounds with different meanings can be made by oneorganism

• sound travels over distances through both air and water

• sound works in dark environments

• the sender and the receiver do not have to be visible to each other

• the sound gives information on the location of the sender

• sound can travel around objects.


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Looking at sound

What are the features of sounds that you hear? Sounds can be loud orsoft and they can have a variety of tones. The most important aspect ofsound that you need to understand for this unit of work is the pitch.You might remember from music that pitch describes how high or low asound is. The best way to look at a sound is to describe sound energy assound waves.

Vibrating objects

When an object vibrates sound is produced. Sound is a form of energythat travels through a medium. The medium vibrates as the energypasses through it.

Vibrations produce compressions (zones where the particles are pushedtogether) and rarefactions (zones where the particles are spread apart) inthe material or medium that it passes through. The figure below showsyou a sound vibration moving forward as a series of compressions andrarefactions. The medium can be a solid, liquid or gas.

one sound wave

r a r e f a c t i o ncompression

A sound vibration traveling forward showing a series of compressions andrarefactions.

The frequency of sound waves is the same as the frequency of the sourcevibrations. The way sound energy travels can be analysed using a modellike the one described below.

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Optional activity: Modeling sound

You will need a slinky spring for this demonstration then follow theseinstructions.

• Attach one end to a fixed object (or get someone to hold one endtightly).

• Stretch the slinky spring until the coil is under tension.

• Compress a small bunch of the spring up near your hand. See thediagram below for details.

• Let go and observe the pulse of energy traveling through the springin a forward direction. You will also notice the way it reflects orbounces back when it hits the end.

compression

compression

compression

rarefaction

rest

rarefaction

The spring represents the medium through which the sound is traveling.

Do exercise 4.2 now.

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Describing a wave

Another way of describing a wave is by using a diagram such as the onebelow. This shows one complete wavelength (rarefaction andcompression). A wavelength is the horizontal length of one cycleof a wave.

One complete wavelength

Continue this wave on by drawing a wave shape pattern so that you draw inanother complete wavelength on this diagram.

Check your answer.

Other aspects of the shape of a wave are the amplitude, and frequency ofthe wave. The amplitude is defined as the height of the wave from aposition of rest to the top of the crest of the wave. The greater theamplitude the louder the sound.

wavelengthamplitude

Frequency is measured in hertz (Hz). This shows the number of cycles(complete wavelengths) that pass a given point in one second.The higher the frequency the higher the pitch of a sound. Pitch is theperception of frequency.

8 Communication

Making a wave

You may like to try this experiment yourself by using one hand to move apen up and down on a sheet of paper while slowly pulling the paper awayfrom the pen with your other hand. Alternatively, have someone else helpyou by pulling the paper as you move the pen up and down.

Repeat the experiment twice making sure you pull the paper away at thesame speed each time. Firstly, model a low sound (pitch) by moving thepen up and down slowly. Then model a high pitch by moving the pen upand down quickly.

Compare the two drawings by describing the differences between them._________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

The waveform gives a lot of information about the sound. The amplitudeof the wave is the loudness of the sound. The frequency (thewavelengths passing a particular point in second) is heard as the pitch ofthe wave. We hear sounds as high and low. High frequency wavesproduce high pitch and we describe the sound as a high sound.Low sounds have a low pitch and a low frequency.

A more scientific way of looking at sound is to use an instrument called acathode ray oscilloscope (CRO).

Cathode ray oscilloscope

A cathode ray oscilloscope is an instrument that allows you to see apictorial representation of a sound wave on a screen.

Sound energy is converted into an electrical signal by a microphone.The microphone in this activity acts a data collector to produce anelectrical signal. This signal is fed into the CRO input where it producesa curve on a screen. Here is a picture or trace of a sound made by ahuman voice.

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Human voice trace

Notice how it doesn’t look smooth but it does have regularity. This isbecause voice is made up of a mixture of waves each having adifferent pitch.

If you use an instrument such as a tuning fork that can produce a singlepitch the image produced by the CRO will look more like this.

Sound 1

Now you can analyse these waves better because they are clearer.

10 Communication

What’s the pitch?

The higher the number of waves that pass a point in a second the higherthe pitch of the sound. If you are looking at sound waves of differentpitch and the CRO settings are identical then the higher pitched soundwill have more wavelengths on a trace.

Below is a picture of a higher pitch sound recorded on the same CRO asthe one above with exactly the same settings.

Sound 2. Higher frequency, higher pitch and reduced loudness whencompared to Sound 1.

Record the number of crests of the waves in both traces above.

Sound 1 = crests

Sound 2 = crests

Check your answers.

Just by counting the number of waves you will notice that there are morein this one for the same amount of space.

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The two sounds that produced these traces can be compared in thetable below.

Feature Sound 1 Sound 2

frequency less greater

pitch lower higher

amplitude higher lower

volume louder softer

You are required to perform a first-hand investigation and gatherinformation to analyse sound wave forms.

You can complete this activity by using a digital oscilloscope program thatyou can download from the Internet. To see a site where you can downloada digital oscilloscope program visit the LMP Science Online webpage at:http://www.lmpc.edu.au/science

If you are able to download a program from the Internet to analyse soundwaves you will need to use a microphone to input the sound signal toyour computer. If you don’t have a microphone use the bud earphonesfrom a walkman radio plugged into the microphone input on yourcomputer. The small speaker can act as a microphone.

Explore the waveforms by carrying out the following:

• speak into the microphone and observe the waveform

• make a high-pitched sound

• make a low-pitched sound

• speak loudly

• speak softly.

Record the waveforms of each of the above.

If you cannot download a digital oscilloscope then use the diagramsfollowing to answer the questions below.

12 Communication

The three sound waves below all have the same amplitude. They thereforewould all have the same loudness. They have different wavelengths anddifferent frequencies. They would therefore have different pitches.Use your knowledge of waves to describe the sound that you would hear foreach of the three waves below.

2

9

1

2

-1

-2

87654321

2

9

1

2

-1

-2

87654321

2

9

1

2

-1

-2

87654321

Trace 1

Trace 2

Trace 3

Trace 1

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_________________________________________________________

_________________________________________________________

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Trace 2

_________________________________________________________

_________________________________________________________

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_________________________________________________________

Trace 3

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answers.

Do Exercise 4.3.

14 Communication

Making sounds

To be able to communicate, animals have to be able to produce differentsounds. In humans, sounds are made by a combination of the lungs, thenasal cavity, the voice box, the lips, the tongue and the hard andsoft palates.

The human larynx

Another name for the voice box is the larynx. It is located in the throat.If you feel your neck you will notice some hard bumps. These arecartilage that forms the outer structure of the trachea (windpipe).The larynx is located towards the top of the trachea.

Adam’s apple

larynx

cartilage

Location of the larynx

epiglottis

hyoid bone

thyroid cartilageor Adam’s apple

vocal ligament

cricoid cartilage

tracheatracheal cartilage

Structure of the larynx

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The larynx is also made up of rings of cartilage. Within the cartilagethere are the vocal cords. As you have already read, sound is the resultof vibrations. Therefore to produce sound it is necessary to producevibrations. This function is done by the vocal cords.

As you breathe in and out the vocal cords are open. When you start totalk the vocal cords close and the air passing through causes them tovibrate. My changing the shape of the vocal cords and the interaction ofthe other organs involved in speech (tongue, mouth, respiratory system)it is possible to get a vast array of sounds.

closedopen

Open and closed vocal cords

Do Exercise 4.4.

Structures used for soundcommunication by other animals

To make sound there has to be a mechanism to produce vibrations in thesurrounding medium. The medium may be air or water. There are fourcommon methods that animals use to produce sound. These are:

• vibrating a membrane in a flow of air

• vibrating a membrane like a drum

• stridulating

• hitting or slapping a surface.

Vibrating a membrane in a flow of air

This is the method used by frogs and mammals. The larynx contains thevocal cords, which vibrate to produce different sounds. Air flows past amembrane and the frequency of the vibration can be changed by themuscles that contract and relax the membrane.

16 Communication

Birds have a similar structure called the syrinx. It contains a membranethat vibrates as air passes. The syrinx is located further down therespiratory system than the larynx and is located at the junction of thetwo bronchi. This means that birds can get their sound from two sourcesof air and can sing for long periods of time by alternating between thetwo air sources while breathing from the other. Dolphins have a larynxthat does not have vocal cords but it is thought that the whistles thatdolphins make come from the larynx while the clicks come from thenasal sac. This produces ultrasonic sound that is used for bothcommunication and navigation.

Vibrating a membrane like a drum

Many insects such as cicadas have a membrane called a tymbal that theyvibrate directly through muscles.

Stridulating

In many organisms there is a stridulatory organ. This consists of ascraper or small peg that is struck against a file like structure. Pitch ischanged depending on how fast the two structures move against eachother. Examples of animals that have stridulatory organs are crickets,grasshoppers and ants.

Hitting or slapping a surface

Some animals slap surfaces to give off signals. For example, beavers,woodpeckers and termites.

As far as sound communication goes there are a variety of structures used bydifferent animals for the production of sound. Gather and processinformation from secondary sources to outline and compare some of thestructures used by animals other humans to produce sound.

Hint

This can be done by using a search engine on the Internet or by visiting alocal library for books and journals. You can also use the informationabove. The information can be processed by using a table such as theone in Exercise 4.5.

Some useful starting points have already been gathered for you on the LMPScience Online webpage at: http://www.lmpc.edu.au/science

Do Exercise 4.5 to finish this part of the module.

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Summary

During this part of the module you should have carried out the followingfirst-hand investigation.

First-hand investigation• Plan and perform a first-hand investigation to gather data to identify

the relationship between wavelength, frequency and pitch of asound.

During this part of the module you should have carried out the followingtasks using secondary information.

Secondary information• Gather and process information from secondary sources to outline

and compare some of the structures used by animals other thanhumans to produce sound.

Summary of content

Sound is a useful and versatile form of communication.Vibrating objects produces sound. The frequency of the sound isthe same as the frequency of the vibration of the source of the sound.In humans the larynx produces sound. Other animals use differentmethods to produce sound including stridulating andvibrating membranes.

18 Communication

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Suggested answers


Describing a wave

Making a wave

Moving the pen up and down slowly produces a longer wavelength thanmoving the pen quickly up and down.

What’s the pitch?

The first trace had 16 crests while the second had 26 crests.

Trace 1 would have a high pitched sound but equal loudness.

Trace 2 would have a lower pitched sound than Trace 1 butequal loudness.

Trace 3 would have the lowest of the three sounds but equal loudness.

20 Communication

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Exercises - Part 4


Exercise 4.1: Sound energya) Explain why sound considered to be a useful and versatile form of

communication?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Identify three examples of how animal use the versatility of sound.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

22 Communication

Exercise 4.2: Vibrating objects

How are sound waves produced?

What is the relationship between the frequency of a sound and thefrequency of the vibration of the source of the sound?

_________________________________________________________

_________________________________________________________

_________________________________________________________

Exercise 4.3: Describing a wave

Label the diagram to show the wavelength and amplitude of the wave.

Define the following terms:

wavelength

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

pitch

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

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frequency

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

amplitude

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Identify the relationship between pitch and frequency. How does thisrelate to wavelength?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Exercise 4.4: The larynxa) Name the structures of the human body that are involved in

sound production.

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Outline the structure of the larynx.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

24 Communication

Exercise 4.5: Animal sound production

Fill in the table below with the information you have gathered about thedifferent structures animals use to produce sound. The first one is donefor you.

Animal Method of sound production

Human Vocal cords within the larynx open and close. This causes theair to vibrate, which produces different sounds.

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Communication

Part 5: What’s this ear?


AMENDMENTS

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Part 5: What’s this ear? 1

Contents

Introduction ............................................................................... 2

Detection of vibration................................................................. 4

Insects...................................................................................................4

Fish .......................................................................................................6

Mammals .............................................................................................8

The frequency range ...........................................................................9

The ear ................................................................................... 12

Outer ear.............................................................................................13

Middle ear ...........................................................................................13

Inner ear .............................................................................................15

The role of the Eustachian tube.........................................................17

Sound shadow....................................................................................20

Hearing devices ...................................................................... 21

Hearing aids .......................................................................................21

Cochlear implants...............................................................................22

Summary................................................................................. 25


Exercises – Part 5 ................................................................... 29

2 Communication

Introduction

The previous part of the module looked at sound as a veryimportant form of communication for humans and other animals.Different methods of creating sound were examined. In this part of themodule the other end of sound communication is looked at, the detectionof sound. The human ear is a complex organ that has a role in balance aswell as hearing. Other organisms may have different methods ofsound detection.

When the ear does not work there are artificial ways ofimproving hearing.


• outline and compare the detection of vibrations by insects, fish andmammals

• describe the anatomy and function of the human ear, including:

– pinna

– tympanic membrane

– ear ossicles

– oval window

– round window

– cochlea

– organ of Corti

– auditory nerve

• outline the role of the Eustachian tube

• outline the path of a sound wave through the external, middle andinner ear and identify the energy transformations that occur

• describe the relationship between the distribution of hair cells in theorgan of Corti and the detection of sounds of different frequencies

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• outline the role of the sound shadow cast by the head in the locationof sound.


• gather, process and analyse information from secondary sources onthe structure of a mammalian ear to relate structures to functions

• process information from secondary sources to outline the range offrequencies detected by humans as sound and compare this rangewith two other mammals, discussing possible reasons for thedifferences identified

• process information from secondary sources to evaluate a hearingaid and a cochlear implant in terms of:

– the position and type of energy transfer occurring

– conditions under which the technology will assist hearing

– limitations of each technology.


4 Communication

Detection of vibration

Sound waves are vibrations of molecules. Humans and other mammalshave ears as receptors for sound vibrations. Other organisms use avariety of structures to detect vibrations. Regardless of the structurehearing is dependent on mechanoreceptors. These are usually hair cellsin a fluid.

Insects

In Australia you are used to the sound of insects throughout the summer.The song of cicadas, crickets and grasshoppers may reach such alevel of sound that it is difficult to hear conversations comfortably.Or sometimes it is only when the sound stops that you hear it.These sounds are communicating information and for this to occurinsects have developed different organs of sound detection.

Unlike mammals, which have easily identified ears, insects have hearingorgans in many different parts of their bodies. The illustration below is acomposite of different hearing organs and their locations in insects.

The location of sound detection organs found in insects.

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Three of the main types of sound detection organs in insects are:

• tympanic organs

• auditory hairs

• vibration receptor.

Tympanic organs

The tympanic organ consists of a membrane stretched across an air sac.In grasshoppers, the tympanic organs are located on the legs. This organworks in a similar way to the mammalian ear. When sound waves reachthe tympanic organ the membrane vibrates and this stimulates the haircells attached to the inside of the membrane and a message is sent via anerve to the brain. These insects move their legs to pick up the mostintense signal.

Insect with tympanic organ on leg. (Photo: David Stanley)

6 Communication

Auditory hairs

Many insects are covered in auditory hairs that are sensitive to soundwaves. These have different lengths and stiffness and respond tovibrations at different frequencies. The hairs are connected to nerve cellsand are particularly abundant on the antennae and legs. Mosquitoes haveauditory hairs on their antennae. Male mosquito can detect femalemosquitoes by the buzz of their wings using these hairs. A tuning forkwith the same frequency as the buzz of female mosquitoes will attractmale mosquitoes.

Vibration receptor

Insects that fly at night have adaptations that can detect ultrasonic soundproduced by bats. Hawk moths hear the ultrasonic sound of bats throughtwo sets of modified mouthparts. One set of mouthparts form an air-filled chamber while the other is a brush-like organ. These organs detectultrasound at the same frequency as the bats that prey upon them.

Give three examples of sound perception organs in insects. What do all ofthese organs have in common?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answers.

Fish

Before the invention of sonar and hydrophones to listen to soundunderwater, it was thought that the depth of the ocean was a quiet place.Looking around at fish there were no visible ears to be seen.However, nothing could be further form the truth as there is large rangeof underwater sounds that are beyond the hearing frequency of humans.With all this sound going on where were the sound perception organs onaquatic animals?

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Fish have several different organs to detect sound waves. These include:

• internal ears

• lateral line organ

• swim bladder amplification.

Internal ears

Fish have an ear but unlike mammals they do not have an externalopening or an eardrum. This adaptation relates to physical properties ofsound waves. Sound travels about four times faster in water than air andthe soft tissue of fish has the same acoustic properties as water.Therefore the sound travels directly through the soft tissues of the fishwithout needing an external opening.

Once the sound reaches the internal ear there are two structures. One isinvolved in balance (labyrinth) the other containing otoliths is involvedin sound perception. Otoliths and the labyrinth make up the inner ear offish. Otoliths are made from calcium salts and are suspended over agelatinous membrane that is covered in sensory hair cells. Otoliths are adifferent density to the rest of the fish tissue so they vibrate more slowlythan the rest of the tissues as sound waves pass through the fish.The movement of the otolith across sensory hair cells is interpreted assound by the fish.

Lateral line

Along the body of fish and extending over the head is a visible line calledthe lateral line. This line is capable of sensing low frequency vibrationsin water. It consists of fluid-filled canals below the surface of the skinwith tiny pores that are open to the exterior.

Fish with lateral line organ. (Photo: Jane West)

Within the fluid-filled canals are collections of sensory hairs(mechanoreceptors) called neuromasts. These respond to low frequencysound. The neuromast consists of hair cells covered with a gel-like

8 Communication

cupula. When there is movement in the fluid in the lateral line the cupulais moved and this stimulates the hair cell to fire off an impulse along theattached nerve to the brain.

The swim bladder

The swim bladder is an organ in fish that is primarily responsible forequalising pressure between the surrounding water and the fish. It is anextendable air sac. A fish swimming uses the swim bladder to maintainbuoyancy. In some fish there is a close association between the swimbladder and the internal ear. The swim bladder acts as an amplifier toany sound, passing the vibrations directly onto the inner ear.

In some fish such as catfish and goldfish, there are a series of four smallbones (Weberian apparatus) that connect the swim bladder directly to theinner ear. Hair cells in the inner ear detect the sound.

Give three examples of sound perception organs in fish. What do all ofthese organs have in common?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answers.

Mammals

Mammals have ears to detect sound. These ears are located either side ofthe head allowing directional information to be acquired. Sound entersthe ear, and travels along the auditory canal. It then causes the tympanicmembrane to vibrate at the same frequency as the sound waves. In themiddle ear the ossicles (small bones) transfer and amplify the soundvibrations to the oval window. The oval window transfers the soundvibrations to the fluid-filled cochlea. Inside the cochlea is the organ ofCorti. This has rows of hair cells that respond to different frequenciesand transfer the message to brain via the auditory nerve.

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All of the organisms above have specialised hair cells that act asmechanoreceptors for sound waves. The difference is in the type andlocation of the organ of hearing.


The frequency range

Different organisms have the ability to hear a range of soundfrequencies. For example, some fish have a small frequency range from2 to 500 Hz. Other animals such as whales and dolphins havefrequency ranges that go from 10 to 100 000 Hz. Dogs hear between60 to 45 000 Hz.

Establishing hearing frequency ranges in animals is very difficult.It often means that the animal has to be trained to respond to a signal asanimals are not capable of directly reporting if they hear a sound.The table below gives the approximate frequency ranges of somemammals hearing.

Animal Frequency range (Hz)

human 20–25 000

dog 67–45 000

cat 45–64 000

bat 2 000–110 000

Beluga whale 1 000–123 000

elephant 16–44 000

dolphin 75–150 000

mouse 1 000–91 000

rat 200–76 000

If you go to different sources you will find differences to these frequencyrange. Even within a species different individuals have different ranges,for example some breeds of dogs have different hearing ranges.

10 Communication

Human frequency range

Humans can hear in the range 20 to 20 000 Hz. Younger children canhear frequencies up to 25 000 Hz but this ability decreases with age.A typical male about 40–years of age can hear sounds up to about17 000–18 000 Hz.

Bat frequency range

If you have ventured out at night you may have heard the high-pitchedsqueaks of bats. As well as these noises, bats flying around at night areemitting sound that is well above the human ability to hear. Bats emithigh frequency sound that they use to navigate in the dark. Solid objectsreflect the sound waves back and these are detected by the specialisedears of the bats.

Bats produce sound in 2 000 to 110 000 Hz range through their mouthsor through elaborate nose organs. The insect-catching bats useecholocation to locate their prey in mid air. To do this they send outhigh frequency sound (ultrasonic) and then interpret the echo thatbounces back. This gives them information on the distance and thedirection of movement.

Whale frequency range

Whales, dolphins and porpoises belong to a group of aquatic mammalsknown as cetaceans. They are further divided into toothed whales(eg. dolphins, Orcas) and baleen whales (eg. Humpbacks, Blue whales).Toothed whales have a very high frequency hearing range while baleenwhales have very low frequency hearing. Both of these groups havespecialised inner ears. They have more nerve endings than terrestrialanimals with toothed whales having more than baleen whales.

There are differences in the thickness of the basilar membrane in theinner ear. A thicker membrane is an adaptation for high frequencysounds. Toothed whales have adaptations for very high frequency sounddetection such as a thick basilar membrane and bony supports for thecochlea. Baleen whales have a very elastic basilar membrane. This is anadaptation for low frequency sound detection.

To hear some animal sounds visit the LMP Science Online webpage for thismodule at: http://www.lmpc.edu.au/science

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Reasons for different ranges

Sound becomes important in environments where visual information islimited. It plays an important role in finding mates, prey and avoidingpredators. Bats use sound to navigate in dark environments to avoidobjects and to locate prey. They use high frequency sound which is onlyuseful over short distances. Humpback whale songs can be heard from100 kilometres away. This helps to keep the groups in contact and tolocate other members of the species for mating. The frequency ofHumpback hearing is in the low frequency range to be able to detect thesound of other whales. Other groups of toothed whales such as dolphinshave high frequency hearing. High frequency sound is used over shortdistances to locate prey.

Process information from secondary sources to outline the range offrequencies detected by humans as sound and compare this range with twoother mammals, discussing possible reasons for the differences identified.

Hint

The information above is useful and there are some good starting points onthe LMP Science Online webpage at: http://www.lmpc.edu.au/science

A good way to process the information is to use a graph to display theinformation from a hearing frequency table. Go to Exercise 5.2 to carry outthis activity.

12 Communication

The ear

You may have been to the doctor with an ear problem and have beentold that you have a middle ear infection. What does that mean?Knowing the structure and function of the ear will help to answerthis question.

The human ear is an organ that has two functions, balance and thedetection of sound. In this part of the module the detection of sound willbe discussed.

The ear can be divided into three sections:

• the outer ear

• the middle ear

• the inner ear.

Find these three areas in the diagram below.

inner earmiddleear

outer ear

The three major areas of the ear

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Outer ear

The outer ear is the part that you can see from the outside and by lookinginto the ear canal. It starts at the external ear and ends at the eardrum.

Anatomy

The outer ear consists of the fleshy organs located on the side ofyour head that you call your ears, the ear canal and the eardrum.The scientific names for these parts are pinna (external part of the ear)auditory canal (ear canal) and tympanic membrane (eardrum).Locate these structures on the diagram below.

pinna auditorycanal

outer ear

tympanicmembrane(eardrum)

Structures of the outer ear.

Function

The pinna collects sound waves and channels the sound into the ear.From here the vibrations travel along the auditory canal until they reachthe eardrum. Here they cause the tympanic membrane to vibrate at thesame frequency as the incoming sound waves. The sound waves in airhave been changed into vibrations in a solid (the tympanic membrane).

Middle ear

The middle ear is an air-filled chamber that contains the ear ossicles andthe Eustachian tube. It lies between the eardrum and the oval window.

14 Communication

Anatomy

The ear ossicles are three tiny bones that are found in the middle ear.They are named after their shapes. You may recall the names hammer,anvil and stirrup. The scientific names for these bones are the malleus(hammer), incus (anvil) and stapes (stirrup). The stapes is the smallestbone in the human body. Also in the middle ear is the Eustachian tube,which has a role that will be discussed later. Locate these structures onthe diagram below.

Eustachian tube

stapes

middleeartympanic

membrane

malleusincus

Structures of the middle ear.

Function

The function of the middle ear is to transmit and amplify the vibrationsfrom the outer ear to the inner ear. The first of the ossicles, the hammeris attached to the tympanic membrane and vibrates at the same frequencyas the vibrating tympanic membrane. The vibrations then pass through tothe anvil and the stirrup. These tiny bones act as levers and magnify thevibrations by up to twenty-two times. The stirrup is attached to the ovalwindow, which lies between the middle and the inner ear. As the stirruppushes against the oval window the vibrations are transmitted through tothe fluid in the inner ear.

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stapes

connects to theoval window of

the cochlea

incus

tympanic membrane(eardrum)

malleus

The three ossicles of the middle ear, malleus, incus and stapes.

Inner ear

The inner ear is located within the bone of the skull. It consists of fluidfilled chambers called the semicircular canals and the cochlea. It extendsfrom the oval window to the auditory nerve.

Anatomy

The oval window is a membrane that separates the middle and inner ear.The fluid filled inner ear contains the semicircular canals and thecochlea. The semicircular canals are involved in balance. The cochlea isthe sense organ of hearing. It is a spiral tube, about the size of a pea, andsimilar in shape to a snail’s shell (thus the name which means snail). It isdivided into three parts, which are separated by two membranes.Find these structures on the diagram below.

oval window

round window

cochlea

auditory nerve

semicircular canals

inner ear

Structure of inner ear.

Within the cochlea is the organ of Corti. The organ of Corti has haircells located on the basilar membrane. These hair cells have cilia that arein touch with another membrane called the tectorial membrane.

16 Communication

Function

As the vibrations from the stirrup push on the membrane of the ovalwindow the vibrations are transferred into waves in the liquid filledchambers of the cochlea. The round window allows the liquid in thecochlea to bulge outwards allowing movement in the fluid within thecochlea. Depending on the frequency and amplitude of the sounddifferent receptors (hair cells) within the organ of Corti are stimulatedand fire a nerve impulse that travels along the auditory nerve to beinterpreted by the brain. The hair cells in the organ of Corti transduce(transfer energy from one medium to another) the energy of vibratingfluids into action potentials in the nerves.

cochlea

auditory nervesemicircular canals

oval window round window

The inner ear

Gather, process and analyse information for secondary sources on thestructure of a mammalian ear to relate structures to functions.

Hint

To do this use a search engine to look for the structure and function ofthe human ear on the Internet. Use search terms such as ‘humanear+structure’. Another good source of information would be Biologytextbooks. Use the index to find the correct page. Or use the informationgiven above.

Analyse the information by relating structure to function. For example,the auditory nerve links the ear with the brain therefore allowing thetransmission of signals between the two organs. The tympanicmembrane is a thin membrane stretched across the ear canal.Its flexibility allows it to vibrate when sound waves enter the ear.The pinna is shaped so that it picks up sound waves but blocks soundsthat are coming from behind the head. This allows the direction ofsound to be determined.

Process the information by completing the table in Exercise 5.3.

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The role of the Eustachian tube

You may have had the experience of your ears ‘popping’ when you go upa mountain or dive to the bottom of a swimming pool. This is caused byrapid air pressure adjustment in the Eustachian tube. The Eustachiantube connects the middle ear with the back of the throat. It is filled withair and responds to changes in pressure. The role of the Eustachian tubesis to keep the pressure in the middle ear and the throat and therefore theoutside atmosphere equal and to drain the middle ear. It also replaces theair in the middle ear after it has been absorbed.

From your understanding of the structure of the ear you should now havea better understanding of where a middle ear infection would occur andhow bacteria could gain access into the middle ear.

Do Exercise 5.4 looking at the role of the Eustachian tube.

The organ of Corti

The organ of Corti detects the different frequencies or pitch of sound.This is achieved by the sensory hair cells that are arranged in parallelrows along the basilar membrane. This membrane is about 2.4 cm longand lies coiled within the cochlea. There are more than 15 000 hair cellsin the organ of Corti. Different hair cells respond to different frequenciesof sound. Each hair cell has stereocilia which look like tiny hairs (thusthe name hair cells) attached at the end.

Rows of hair cells in the organ of Corti.

The last of the ossicles (stapes) causes the oval window to vibrate andthis sends pressure waves into the fluid in the cochlea. Pitch is a functionof the wave frequency of sound waves. It is recognised in the organ ofCorti because the basilar membrane is not uniform along its length. It isthicker and less flexible at the start of the organ of Corti and narrow andmore flexible at the other end of the membrane. Different frequenciesbend the basilar membrane along it length. When a region of the basilar

18 Communication

membrane is stimulated by a particular frequency of sound the basilarmembrane moves upwards (flexes) and the stereocilia then contact thetectorial membrane. High frequency sound waves flex the membrane ashort distance along the membrane while low frequency sounds travelsfurther into the cochlea. The volume of the sound (amplitude of thesound waves) increases the number of hair cells that are bent and resultsin more nerve impulses to the brain.

The stereocilia that responds fires off a message to the brain.The combination of hair cells that fire gives information about thefrequency, intensity and length of the sound wave and is theninterpreted to be a particular sound.

hair cell

stereocilia

tectorial membrane

basilar membrane

The organ of Corti


Path of sound

Sound enters the ear at the pinna as energy in the form of sound waves ina gas. When the sound waves reach the tympanic membrane the energyis changed into vibrations in a solid. The energy is then transferred andamplified by the ossicles in the inner ear. At the oval window the energyis transferred to vibrations in a fluid in the cochlea of the inner ear.Here the energy is transduced into electro chemical energy by thestereocilia of the hair cells. The stereocilia are attached to neurones.The axons of the neurones join together to form the auditory nerve.

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outer ear sound energy

middle ear mechanical energy

inner ear electro-chemical energy

Energy transformations in the ear

Trace the path of sound through the ear by using the following words to fillin the blanks below.

cochlea, middle, tympanic, ossicles, hair, malleus, pinna, incus, stapes,organ of Corti, auditory

When sound waves enter the_____________ they travel along the

auditory canal and cause the ___________________ membrane

(eardrum) to vibrate. These vibrations are carried and amplified by the

_____________in the____________ ear. The ossicles are three tiny

bones also known as the ______________ (hammer), the

_________________ (the anvil) and the ____________ (the stirrup).

The ossicles join the inner ear at the oval window. The ____________ is

a snail-shaped, fluid-filled structure in the inner ear. Inside the cochlea is

another structure called the ________________________. Inside the

organ of Corti there are _________ cells located on the basilar

membrane. These are in contact with the tectorial membrane. When

vibrations reach the hair cell the message is converted into an electro-

chemical response which travels via the ____________nerve to the brain.

Check your answers.

Do Exercise 5.6.

20 Communication

Sound shadow

When a human hears a sound there is information about the direction ofthe sound. This comes from the location of the ears on either side of thehead. If the volume of the sound is the same then the sound is comingfrom straight ahead. If it is to the left then the stimulus reaching the leftear will be greater than the stimulus that arrives at the right ear.There will also be a slight time delay. This is because the head forms asound shadow.

sound source

sound shadow

The sound shadow

The sound waves have to travel around the head to the opposite ear.The brain interprets the difference between the waves arriving at each earand the direction of sound is then known. When you hear a sound youusually turn your head so that the sound is equal in both ears at that pointyou will looking in the direction of the source of the sound.

Do Exercise 5.7.

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Hearing devices

When hearing is not working efficiently there are some devices that canimprove or return hearing. Two of these devices are:

• hearing aids

• cochlear implants.

Hearing aids

Hearing aids are small electrical devices that sit behind the ear.They consist of a microphone, an amplifier, a receiver and a speaker.The hearing aid takes sound waves arriving at the ear, increases thevolume and redirects the sound into the ear.

Position and type of energy transferoccurring

Hearing aids detect sound waves. The energy is then transferred toelectrical energy which is then transformed back into sound waves whichare amplified into the auditory canal.

Conditions under which the technology willassist hearing

Hearing aids are useful when there has been damage to the outer andmiddle ear. They will not improve hearing if there has been damage tothe inner ear. The technology is much cheaper than the cochlear implantand does not have the risks associated with surgical treatments.

22 Communication

Limitations of technology

Hearing aids are amplifiers, making the sounds in the environmentlouder. Louder does not necessarily lead to better hearing. Hearing aidsare a simple device that are relatively cheap but some people find themannoying as they amplify all sound including background noise.

Cochlear implants

Cochlear implants are also known as the bionic ear. This is an Australianinvention by Dr Graeme Clark. They consist of external parts andsurgically implanted parts. They return a sense of hearing to people whohave damaged middle or inner ear function.

Position and type of energy transferoccurring

The external parts include a microphone, speech processor and atransmitter. The microphone picks up sound waves and sends themto the speech processor. This is usually located behind the ear or ina pocket.

Sound waves are picked up by the microphone and are processed by thespeech processor into an electrical signal. The speech processor is acomputer that digitises the sound. This signal is then sent to thetransmitter coil located on the outside of the ear. FM radio wavestransfer the signal to the implanted receiver. This then transmits thesignals to the electrodes inside the cochlea which is interpreted by thebrain. The electrodes stimulate the nerve fibres in the auditory nerve.

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microphonehook over ear

speechprocessor

transmitting coil (sends FM radiowaves through skin to implant)

ear drum

electrode stimulates nerveendings inside cochlea

implant receives radiowaves (and sends signals

through electrode)

The cochlear implant

Conditions under which the technology willassist hearing

Cochlear implants are particularly useful to people who have sustainedmiddle ear damage or damage to the hair cells in the middle ear.These people would not benefit from traditional hearing aids.The cochlear implant directly stimulates the auditory nerve therefore by-passing the hair cells.

Limitations of technology

The cochlear implant does not help all people with hearing difficulties.It has some limitations including:

• it is different from hearing sound

• it requires the person to learn to interpret the sensations they receive

• it takes time and experience for this to occur.

There are also risks associated with the surgery that requires ageneral anaesthetic including risks to the facial nerves and the chanceof infection.

24 Communication

Process information from secondary sources to evaluate a hearing aid and acochlear implant in terms of:



– limitations of each technology.

Hint

Use Biology textbooks, CD ROMs or the Internet to search for informationon hearing aids and the cochlear implants. There are some useful sitesgathered for you on the LMP Science online webpage for this module at:http://www.lmpc.edu.au/science

The information above would also be useful.

Use the table in Exercise 5.8 to process the information from secondarysources on technologies that assist hearing.

This completes Part 5 of Communication.

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Summary

There were no first-hand investigations in this part of the module.

However, during this part of the module you should have carried out thefollowing three tasks using secondary information.

Secondary information• Gather, process and analyse information from secondary sources on

the structure of a mammalian ear to relate structures to functions.

• Process information from secondary sources to outline the range offrequencies detected by humans as sound and compare this rangewith two other mammals, discussing possible reasons for thedifferences identified.

• Process information from secondary sources to evaluate a hearingaid and a cochlear implant in terms of:



– imitations of each technology.

Summary• Organisms have different ranges of frequency in their hearing.

• Hair cells are the sense organs that detect sound in animals but theseare found in different types of organs.

• The structure of the mammalian ear is related to the function ofhearing and balance.

• The Eustachian tube equalises the air pressure between the ear andthe back of the throat.

• Sound waves arrive at the ear and are changed to vibrations in thetympanic membrane. The ossicles transfer these vibrations to thecochlea via the oval window. The hair cells in the organ of Corti

26 Communication

respond to specific frequencies. This information is changed intoelectro chemical impulses which travel via the auditory nerve to thebrain where the sound is interpreted.

• The sound shadow cast by the head assists in the location of soundby comparing the different signals that arrive at each ear.

• When there are hearing difficulties some devices such as hearingaids and the cochlear implant may be useful to restore hearing.Each of these has specific uses and limitations.

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Suggested answers


Insects

Examples of sound perception organs in insects are tympanic organs,auditory hairs and modified mouthparts. All of these organs havesensory hairs.

Fish

Examples of sound perception organs in fish are internal ears, lateral lineorgan and swim bladder amplification. In all cases it is sensory hairs thatare associated with the perception of sound.

Fill in the blanks

When sound waves enter the pinna they travel along the auditory canaland cause the tympanic membrane (eardrum) to vibrate. These vibrationsare carried and amplified by the ossicles in the middle ear. The ossiclesare three tiny bones also known as the malleus (hammer), the incus (theanvil) and the stapes (the stirrup). The ossicles join the inner ear at theoval window. The cochlea is a snail-shaped, fluid-filled structure in theinner ear. Inside the cochlea is another structure called the organ ofCorti. Inside the organ of Corti there are hair cells located on thebasilar membrane. These are in contact with the tectorial membrane.When vibrations reach the hair cell the message is converted into anelectro chemical response which travels via the auditory nerve tothe brain.

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Exercises - Part 5


Exercise 5.1: Detection of vibrationa) Outline the detection of vibrations by insects, fish and mammals.

Insects _______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Fish _________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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Mammals _____________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Compare has a specific meaning for your Biology course. It isdefined as ‘show how things are similar and different’. To answerthis question describe how the detection of vibrations by insects, fishand mammals are similar and how they are different.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Exercise 5.2: Frequency of hearinga) Use the table and graph paper below to graph the hearing

frequencies of a range of organisms. You may choose to use aspreadsheet program if you have access to one.

Animal Frequency range (Hz)

human 20–25 000

dog 67–45 000

cat 45–64 000

bat 2 000–110 000

Beluga whale 1 000–123 000

elephant 16–44 000

dolphin 75–150 000

mouse 1 000–91 000

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b) Name two of the organism above and compare the frequency rangewith that of humans. What possible reasons can you suggest for thedifferences observed?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Exercise 5.3: The eara) On the diagram below label the following structures: the outer,

middle and inner ear, pinna, tympanic membrane, ear ossicles, ovalwindow, round window, Eustachian tube, cochlea, auditory canal,auditory nerve.

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b) Fill in the table outlining the anatomy and function of structures ofthe ear.

Structure Anatomy Function

pinna

tympanic membrane

ear ossicles

oval window

round window

cochlea

organ of Corti

auditory nerve

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c) Choose three of the structures above and describe how the structureis related to the function.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Exercise 5.4: The role of the Eustachian tube

Outline the role of the Eustachian tube.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Exercise 5.5: The organ of Corti

Describe the relationship between the distribution of hair cells in theorgan of Corti and the detection of sounds of different frequencies.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

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_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Exercise 5.6: Path of sound

Trace the path of a sound wave through the external, middle and innerear and identify the energy transformations that occur.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Exercise 5.7: The sound shadowa) What is the sound shadow?

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Outline the role of the sound shadow cast by the head in the locationof sound.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

36 Communication

Exercise 5.8: Hearing devicesa) Fill in the table below to illustrate the differences between hearing

aids and the cochlear implant.

Feature Hearing aid Cochlear implant

energy transfer

type of hearing loss

limitations

advantages

b) Evaluate the two devices in terms of:

i) the position and type of energy transfer occurring

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

ii) conditions under which the technology will assist hearing

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

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iii) limitations of each technology

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

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Communication

Part 6: It’s all in the head


AMENDMENTS

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Part 6: It’s all in the head 1

Contents

Introduction ............................................................................... 2

The nervous system.................................................................. 3

The neurone .........................................................................................3

The nerve impulse................................................................................8

The brain ................................................................................. 11

Cerebrum............................................................................................11

Cerebellum .........................................................................................13

Medulla oblongata..............................................................................14

Dissection of a sheep’s brain.............................................................14

Looking at a model brain....................................................................20

Interpretation of sensory signals ......................................................22

Summary................................................................................. 25


Exercises – Part 6 ................................................................... 29

2 Communication

Introduction

Once stimuli have been detected it is the function of the nervous systemto transfer the information as electro chemical signals to the relevantparts of the brain for interpretation. There is some practical work to doin this part. You will need a cutting board, a sheep’s brain, a scalpel orknife and newspaper. Alternative exercises are provided.


• identify that a nerve is a bundle of neuronal fibres

• identify neurones as nerve cells that are the transmitters of signals byelectro chemical changes in their membranes

• define the term threshold and explain why not all stimuli generate anaction potential

• identify those areas of the cerebrum involved in the perception andinterpretation of light and sound

• explain, using specific examples, the importance of correctinterpretation of sensory signals by the brain for the coordination ofanimal behaviour.


• perform a first-hand investigation using stained prepared slidesand/or electron micrographs to gather information about the structureof neurones and nerves

• perform a first-hand investigation to examine an appropriate mammalianbrain or model of a human brain to gather information to distinguish thecerebrum, cerebellum and medulla oblongata and locate the regionsinvolved in speech, sight and sound perception

• present information from secondary sources to graphically representa typical action potential.

Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originallyissued 1999. Amended November 2002. The most up-to-date version can befound on the Board’s websites athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html

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The nervous system

For the perception of information to be used there must be a rapid systemof communication within the body of an organism. This task is achievedby the nervous system. The nervous system consists of a coordinatingorgan, the brain and a system of branching nerves that reach to all partsof the body. The basic structure of the nervous system is the neurone(neuron) or nerve cell. Neurones receive the signals from the senseorgans and transmit the information by electro chemical changes in theirmembranes. A bundle of neuronal fibres are known as a nerve.Nerves connect to the central nervous system (CNS) that consists of thebrain and the spinal cord. The transfer of a stimulus from the bodyextremities to the brain takes only milliseconds to occur.

The neurone

Neurones are nerve cells that transmit signals by electro chemicalchanges in their membranes. They consist of a cell body containing anucleus, cytoplasm and organelles, and extensions or processes to eitherend called dendrites and axons.

The neurone transmits the electro chemical signal in one direction only.The axons conduct the signal away from the cell body (an easy way toremember is away and axon both start with the letter a). The dendritestake the signal to the cell body.

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direction of impulse

cell body

dendrites

nucleus

myelin sheath

axon

synaptic terminals releaseneurotransmitters into the synapse

A neurone

Axons

Many neurones only have one axon. Axons are branched at theend leading to many synaptic terminals. These release theneurotransmitters into the gap between neurones called the synapse.Some axons have a fatty insulating material known as the myelin sheathwrapped around the axon. This is part of some specialised cells knownas Schwann cells. Axons may be more than a metre in length, forexample in the sciatic nerve, although some in the brain are lessthan a millimetre. At the end of the axons are sacs that containthe neurotransmitters.

Dendrites

Dendrites are small branch-like projections that connect to other cells.The branching nature increases the available surface area and allowsconnection for incoming impulses. Dendrites can grow and shrinkduring the life of the neurone. Alcohol and old age has been shown toreduce dendrites while a situation where the person is learning canincrease the growth of dendrites. Dendrites are shorter and thinner thanthe axon.

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Types of neurones

There are many different types of neurones but they can be grouped intothree major categories:

• sensory

• motor

• connecting.

Sensory neurones have the dendrites attached to a sensory organ such asthe ear. They change the information form the stimulus such as soundinto an electro chemical response in the neurone. Sensory neurones havetheir axons attached to another neurone.

Motor neurones are in a way the opposite of sensory neurones.They have their dendrites connected to other neurones but their axons areconnected to effector organs such as muscles and glands.

Connecting neurons (interneurones) have both their axons and dendritesattached to other neurones. They are most common in the spinal cordand brain.

The synapse

Between each neurone is a small gap called a synapse. For an impulse tocross the synapse neurotransmitters are released by the axon terminals.Common neurotransmitters are dopamine, histamine and endorphin.When these chemicals reach the dendrites of the next cell it causes thenext neurone to fire. This explains why the signal in neurones isknown as an electro chemical response. Along the neurone the signalis electrical while at the synapse the signal is changed into achemical signal.

The effects of many drugs such as depressants and stimulants affect thetransmission of nerve impulses across the synapses of nerve cells bysuppressing or increasing the release of neurotransmitters.

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direction of signals

synapse

axon

axon terminal

dendrite ofnext neurone

neurotransmitters

The synapse between two neurones

Nerves

Nerves are bundles of nerve fibres (that is dendrites or axons) outside ofthe brain. The fibres are surrounded by myelin which acts as aninsulator. You have already learnt about the auditory nerve and the opticnerve when studying the ear and the eye. These are the collective axonscoming from the hair cells in the cochlea or the rod and cone cells inthe eye.

nerve

axon

connective tissue

blood vessel

A nerve bundle is made up of neuronal fibres.


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Microscopic examination of neurones

Perform a first-hand investigation using stained prepared slides and/orelectron micrographs to gather information about the structure of neuronesand nerves.

If you do not access to a microscope and slides there are some micrographson the LMP Science Online websites at: http://www.lmpc.edu.au/science

There are also some links to pages on the Internet that have moremicrographs including electron micrographs. Below is a micrograph ofsome neurones as seen under a light microscope. The clearest feature in thepicture is the large cell bodies with the darker stained nucleus.

neurone

nucleus

cell body

Light micrograph of nerve cells. (Photo: J West)

In the space below draw a diagram of the above microscopic slide.Label the neurones, cell body and nucleus.

8 Communication

Drawing of micrograph of neurones

Name the features seen on the micrograph of neurones as seen through alight microscope.

_________________________________________________________

_________________________________________________________

Check your answers.

The nerve impulse

When an atom or a group of atoms is electrically charged it is called anion. Some ions within cells are positive (calcium ion Ca+, sodium ionNa+, potassium ion K+) while others carry a negative charge (chloride Cl–

and some proteins). Cells are surrounded by a semipermeable membranethat controls the passage of ions into and out of the cell. In themembrane are ion channels that allow particular ions to pass through.The difference between the concentration of particular chemical ionsinside and outside of a cell results in a negative electrical charge within aneurone. If a positive charge occurs in a neurone it will be passed to thenext neurone as a voltage pulse.

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Resting potential

At rest the inside of a neurone is negative compared to the outside of theneurone. This charge is obtained by potassium ions (K+) passing easilythrough the membrane to the outside while chloride ions (Cl–) andsodium ions (Na+) cannot cross as freely. The negatively chargedproteins within the neurone are also prevented from crossing themembrane. As well as ion channels in the membrane there are ionpumps. These use energy to move more ions across the membrane.All of this results in the resting potential being a negative charge of–70 millivolts within the neurone.

Action potential

An action potential is the name given when a neurone sends an impulseto the next neurone. It occurs when there is a rapid movement ofpotassium and sodium ions across the cell membrane. When a neurone isstimulated the first response is for sodium channels to open and thisresults in sodium ions rushing into the cell. The positive charge on thesodium ions depolarises the cell and the overall negative charge starts tofall towards zero. When it reaches approximately –55 millivolts theneurone will fire and an impulse or spike will occur. This is thethreshold for the reaction. It is a non-graded or ‘all or none’ response.It is called an ‘all or none’ response because there is no variation in theresponse. It either fires completely or not at all. Therefore if thestimulus is not great enough to reach the threshold level the neurone willnot fire. Following the opening of the sodium channels, the potassiumchannels open and potassium moves out of the cell. This repolarises thecell and it moves back towards the resting potential. The time taken toreturn to the resting potential is known as the refractory period.During this time the neurone cannot fire again.

10 Communication

0

–50

–70

Pot

entia

l acr

oss

plas

ma

mem

bran

e (m

V)

Time (ms)

threshold level

resting potentialresting potential

0 1 2 3 4 5 6

refractoryperiod

action potential

Graph of a typical action potential

Present information from secondary sources to graphically represent atypical action potential.

Hint

The diagram above is one example of a graphical representation of a typicalaction potential.

Animations are good graphical representations as well. Visit the LMPScience Online website for this module to view some of these animations at:http://www.lmpc.edu.au/science

Do Exercise 6.2 looking at the action potential of a neurone.

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The brain

The brain is a large organ located within the protective skull. It isimportant as it controls the functioning of the rest of the body. It is thelocation of emotions and thought. Any damage to the brain results inchanges to behaviour and coordination of the body. The three parts ofthe brain that you will be looking at are the cerebrum, the cerebellum andthe medulla oblongata.

cerebrum cerebral cortex

cerebellummedulla oblongata

Three parts of brain: cerebrum, cerebellum and the medulla oblongata.

Cerebrum

The cerebrum is the most obvious and largest part of the brain. It ishighly folded therefore increasing the surface area available within thesmall size of the skull.

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The human brain showing the highly folded nature of the cerebrum.(Photo: © LMP)

When viewed from above the human brain is divided into twohemispheres. The left hemisphere controls the right side of the bodywhile the right hemisphere controls the left side of the body.

The cerebrum is divided into the following lobes:

• frontal

• parietal

• occipital

• temporal.

Locate these lobes of the diagram following.

frontal lobe

temporal lobe

parietal lobe

occipital lobe

Lobes of the cerebrum

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Frontal lobe

The frontal lobes are located behind the forehead at the front of the head.This part of the brain is involved in ‘higher order’ thinking.This includes planning, problem solving and personality. It is thelocation of ‘consciousness’. In the lower part of the left frontal lobe isBroca’s area an important area for speech production.

Parietal lobe

The parietal lobes are at the top of the head towards the back. This areais especially important for interpreting sensory signals including sightand sound.

Occipital lobe

These lobes are located at the back of the head. The occipital lobe isconcerned with vision as well as other perceptions such as touch,pressure, temperature and pain. It is the site of the visual cortex.

Temporal lobe

The temporal lobes are located at the side of the head above the ears.This area interprets the impulses from the ears and gives meaning to theinformation. It is an important region for the sense of hearing.Wernicke’s area is in this region and is responsible for speech andlanguage function.


Cerebellum

Beneath the hemispheres of the brain there is the cerebellum. This partof the brain is concerned with coordination. It receives informationabout the position of joints and muscles. It also has a role in learning andin hand-eye coordination.

14 Communication

Medulla oblongata

The medulla oblogatais part of the brain stem and continues into thespinal cord. It controls functions such as breathing, vomiting, digestionand heart rate.

Perform a first-hand investigation to examine an appropriate mammalianbrain or model of a human brain to gather information to distinguish thecerebrum, cerebellum and medulla oblongata and locate the regions involvedin speech, sight and sound perception.

If you are carrying out a first-hand investigation of dissecting an appropriatemammalian brain such as a sheep’s brain make sure that you have assessedthe possible risks before you start. If you are using a sharp cuttinginstrument be aware of cutting injuries. Have first aid equipment availableto treat any cuts. Have plenty of newspaper to work on and to wrap up thedissection when you finished. Make sure that you dispose of any wastesafely in a garbage bin. Wear covered shoes in case you drop thecutting instrument.

A dissection of a sheep’s brain is available as a webpage on the LMPScience Online web site for this module at: http://www.lmpc.edu.au/science

Dissection of a sheep’s brain

You can obtain a sheep’s brain from your local butcher.

You will need:

• a cutting board

• a sheep’s brain

• a scalpel or knife

• newspaper.

Aim

To carry out a dissection of a sheep’s brain to distinguish the cerebrum,cerebellum and medulla oblongata and locate the regions involved inspeech, sight and sound production.

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Method

Step 1 Place the sheep’s brain on the cutting board.

External features of a sheep’s brain

Without cutting anything examine the outside of the brain and find thefollowing; cerebrum, cerebellum and medulla oblongata.

cerebellum

cerebrum

(Photo: © LMP)

The underside is best to see the medulla oblongata.

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(Photo: © LMP)

Step 2 Cut the brain longitudinally as shown in the photograph below.

Taking a longitudinal section. (Photo: © LMP)

You should be able to see the leaf-like structure of the cerebellum at therear of the brain.

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Leaf-like cerebellum. (Photo: © LMP)

Step 3 Now cut a transverse section across the cerebrum.

Cutting a transverse section of the cerebrum. (Photo: © LMP)

The dark coloured material at the top of the cerebral cortex is the ‘grey’matter. This is where the cell body containing the nucleus of the

18 Communication

neurones is found. The central ‘white’ matter is where the long axons ofthe neurones are located. Identify these regions.

Grey and white matter in the cerebrum. (Photo: © LMP)

Step 4 Locate the regions of the brain that are involved in speech sightand sound production by using the diagrams following.

The temporal lobe of the cerebrum is the auditory cortex. It controls speechand hearing. (Photo: © LMP)

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occipital lobe

The occipital lobe of the cerebrum is the visual cortex. It is involved in sight.(Photo: © LMP)

Results

Draw a longitudinal section of the brain in the space below. Locate andname the cerebrum, the cerebellum and the medulla oblongata. Shade inthe areas involved in speech sight and sound.

Conclusion

A detailed drawing of the sheep’s brain was done showing the location ofthe cerebrum, cerebellum and medulla oblongata and also the regionsinvolved in speech, sight and sound production.


20 Communication

Looking at a model brain

If you are unable to get a sheep’s brain for dissection then the alternativeis to look at a model of a human brain. Below are two photographs ofhuman brain models. The first shows the external features of the brainincluding the cerebrum, cerebellum, medulla oblongata and the spinalcord. Locate all of the features from the photograph.

cerebrum

cerebellum

spinal cord

medulla oblongata

(Photo: © LMP)

If the brain is cut between the hemispheres than the view below canbe seen.

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cerebrum

cerebellum medulla oblongata

corpus callosum

spinal cord

Model of the human brain cut in a longitudinal section. (Photo: © LMP)

As well as these major structural areas there are areas associated withsound or visual perception. These are in the visual cortex and theauditory cortex. Other important areas dealing with sound and visualperception are Broca’s area and Wernicke’s area. These are illustratedon the diagram following.

cerebellum

sensory cortexmotor cortex

frontal lobe

Broca’s area(speech)

temporal lobe(auditory cortex)

brain stem

parietal lobe

Wernicke’s area(comprehension of

language)

occipital lobe(visual cortex)

Diagram of brain areas

22 Communication

Brain area Function

visual association area processing of visual information

visual cortex detection of information from the eye

auditory association area processing of audio stimulus

Wernicke’s area language

auditory cortex detection of sound

Broca’s area speech production

Do Exercise 6.5. Examining a model human brain.

Interpretation of sensory signals

The brain interprets the incoming sensory signals for the organs ofperception throughout the body. Using this information the behaviour ofan animal is coordinated. Behaviour is the actions of an organism. If theinformation is not correctly interpreted this will lead to abnormalbehaviour in the animal.

Any damage to the brain can lead to misinterpretation. Two examples ofincorrect interpretation of sensory signals are:

• Wernicke’s aphasia

• Broca’s aphasia.

Wernicke’s aphasia

The condition was recognized in 1874. A patient who was unable tocomprehend language but was capable of speech was found to have abrain tumor on the brain in this area called Wernicke’s area after itsdiscoverer. This condition may also be caused by stroke or head injury.

Wernicke’s area is usually located on the left side of the brain in thetemporal lobe close to the junction with the parietal lobe. It is not foundin exactly the same location in every brain. It is important inunderstanding language. If there is damage to this area then a conditionknown as Wernicke’s aphasia occurs. People with this condition cannot

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understand language but can still make sounds. They can hear and readwords but not understand the information that is conveyed in thesounds or words. This leads to confusion and this may lead tobehavioural changes.

Broca aphasia

Another important area in sound perception is Broca’s area. It is locatedin the lower part of the left frontal lobe. Damage to this region results inthe understanding of what is said but the inability to produce sounds toreply. The damage prevents people from producing speech or otherwisethe speech is slurred and slow.


This completes the Option Communication.

24 Communication

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Summary

First-hand investigations

There were two first-hand investigations to do in this part:

• perform a first-hand investigation using stained prepared slidesand/or electron micrographs to gather information about the structureof neurones and nerves

• perform a first-hand investigation to examine an appropriatemammalian brain or model of a human brain to gather information todistinguish the cerebrum, cerebellum and medulla oblongata andlocate the regions involved in speech, sight and sound perception.

Secondary information

During this part of the module you should have carried out the followingtask using secondary information.

• Present information from secondary sources to graphically representa typical action potential.

Summary

The interpretation of sensory information occurs in the brain. The basicunit of the nervous system is the neurone or nerve cell. The neuroneconsists of dendrites, the cell body and an axon. Between neurones thereis a gap known as a synapse. The impulse across the synapse involveschemicals known as neurotransmitters. The impulse that travels alongthe neurone is an electrical signal while the crossing of the synapse ischemical. This explains that the nerve impulse consists of electrochemical signals.

A nerve is a collection of neuronal fibres (axons and dendrites). When aneurone sends an impulse it is called an action potential. This follows an

26 Communication

‘all-or-none’ response. After firing a neurone is unable to fire again for acertain period of time known as the refractory period.

The main areas of the brain are the cerebrum, cerebellum and themedulla oblongata. The cerebrum forms a large part of the brain.The areas involved in perception are the visual cortex and auditorycortex, Wernicke’s area and Broca’s area. If the brain is damaged theremay be aphasia and the behaviour of the organism is affected.

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Suggested answers

Your answer should be similar to this answer. If your answer is verydifferent or if you do not understand an answer, contact your teacher.

Microscopic examination of a neurone

The main features visible in the micrograph of neurones as seen througha light microscope are the cell body and nucleus.

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Exercises – Part 6


Exercise 6.1: Nerves and neuronesa) What is a neurone?

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b) In the space below, draw a simple diagram of a neurone labeling thecell body, dendrites, axons, axon terminals, myelin sheath and cellnucleus.

c) What is a nerve?

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d) Draw in the space below a nerve showing the bundles of neuronalfibres.

Exercise 6.2: The action potentiala) Define the term threshold and explain why not all stimuli generate

an action potential.

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b) Describe the transmission of a signal from one neurone to the next.

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c) Draw a graphical representation of an action potential.

0

–50

–70

Pot

entia

l acr

oss

plas

ma

mem

bran

e (m

V)

Time (ms)

threshold level

0 1 2 3 4 5 6

Exercise 6.3: The braina) Name the four lobes of the cerebrum.

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b) For each lobe describe its function.

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Exercise 6.4: Dissection of a sheep’s brain

During your Biology course you would have carried out a dissection off asheep’s brain.

a) Outline the steps you used during the investigation.

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b) What possible risks did you identify and what did you do to reducethese risks?

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Exercise 6.5: Model of a human braina) On the photograph below of a human model brain label the

cerebrum, the cerebellum, the medulla oblongata or the brain stem.

(Photo: © LMP)

b) On the diagram below identify those areas of the cerebrum involvedin the perception and interpretation of light and sound including thevisual cortex, the auditory cortex, Wernicke’s Area andBroca’s Area.

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Exercise 6.6: Interpretation of sensory signals

Explain, using specific examples, the importance of correct interpretationof sensory signals by the brain for the coordination of animal behaviour

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Example 2_________________________________________________

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Student evaluation of the module

Name: ________________________ Location: ______________________

We need your input! Can you please complete this short evaluation toprovide us with information about this module. This information willhelp us to improve the design of these materials for future publications.

1 Did you find the information in the module clear and easy tounderstand?

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2 What did you most like learning about? Why?

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3 Which sort of learning activity did you enjoy the most? Why?

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4 Did you complete the module within 30 hours? (Please indicate theapproximate length of time spent on the module.)

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5 Do you have access to the appropriate resources? eg a computer, theinternet, scientific equipment, chemicals, people that can provideinformation and help with understanding science

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Please return this information to your teacher, who will pass it along tothe materials developers at OTEN – DE.

Learning Materials ProductionOpen Training and Education Network – Distance Education

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