Download - Lec 7-BIO Lab 1021 The Senses rev 6-11 Neurons communicate with our muscles or glands to produce a reaction within our body. They communicate through chemicals.

Lec 7-BIO Lab 102 1

The Senses rev 6-11

• Neurons communicate with our muscles or glands to produce a reaction within our body. They communicate through chemicals called neurotransmitters.

• However, in order to receive a stimulus from the environment, there is a specialized type of neuron called a receptor.

• Sensory input (called a stimulus) causes a change within or outside the body. The receptor accepts the stimulus (a form of energy such as heat, pressure, or sound). and converts the energy into a form that can be understood by the body.

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The Senses

• Receptors are usually categorized by the kind of stimulus to which they respond.– Chemoreceptors are stimulated by chemicals

that attach to receptors at the end of the sensory neuron.• sense of taste and smell.

– Pain Receptors– Mechanoreceptors are the largest class of

receptors and include:

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The Senses-mechanoreceptors

• stretch receptors • proprioceptors• tactile(touch and vibration) • hair cells (ear)• baroreceptors (sensitive to changes in blood

pressure) – Thermoreceptors (temperature)– Photoreceptors (light)

Receptor Adaptation when exposed to the same degree of stimulus, receptors stop sending impulses so you no longer respond to the stimulus.

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The Senses

The EYE• composed of 3 tissue layers

– outer layer is the sclera– middle layer is the choroid– inner layer is the retina

• The Sclera (or white of the eye)– is composed of tough, white connective tissue

that is modified in the front• eye muscles attach to the sclera

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The Senses

– this modified “spot” is called the cornea and is clear so that light can pass through

• cornea is the most exposed part of the eye and is vulnerable to damage from dust, dirt, etc.

• has high ability to regenerate and repair itself– can also be replaced surgically

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The Senses

• Light passes through the cornea and a small fluid filled space called the aqueous humor– the aqueous humor is located between the cornea

and the lens (the anterior chamber of the eye)

– it nourishes and cushions the cornea and lens• The vitreous body or vitreous humor is located

behind the lens (in the posterior chamber of the eye)– this is a gel-like fluid– the fluid transports nutrients and wastes and

maintains the shape of the eye

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The Senses

• Choroid layer– middle layer which contains a large portion of

the blood supply for the eye– is darkly pigmented to absorb light and prevent

it from scattering and reflecting within the eye– Some red light is reflected back from the

choroid however and causes the “red-eye effect” in photographs

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The SensesThe Choroid Layer

– Contains the iris• a ring of smooth muscles that regulates the

opening of the pupil (the central opening of the iris which allows light to enter the eye)

• the iris gives the eye its color– and the ciliary body

• a ring of muscles that encircles the lens and can change the shape of the lens

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The Senses

• The lens• composed of transparent crystalline proteins• focuses the visual image on the retina• is held in the center of the ciliary body by

suspensory ligaments • precise focusing requires thickening or

thinning of the lens • the changing shape allows for focusing on

near or distant objects

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The Senses

• The Retina– innermost layer of tissue which contains 2

kinds of photoreceptors (light sensitive receptors)• RODS sensitive to low levels of light (night

time vision)– Allow us to see in black and white

• CONES require high levels of light– come in 3 varieties (red, green and blue)

so we can see in color


The Senses

– a dense collection of cones, the macula lutea, is found at the back of the eye near the fovea centralis, the center of focus

– anything we wish to see in great detail is focused on the fovea centralis

– the optic disc• blind spot where nerve impulses that have

been focused on the retina exit the eye via the optic nerve


The Senses

• Eye Protection– bony socket of the skull– layer of adipose tissue that cushions the socket– blinking– tears from the lacrimal gland cleanse, lubricate

and protect the eye• tears contain mucus, antibodies and

lysozyme, a bacteria destroying enzyme• the lacrimal ducts take excess tears from the

eyes and drain them into the nose


EYE DISSECTION-SAFETY

• may get splashed as you open the eye• Dissection

– follow instructions on page 91 of text


The Ear

• Is an organ of both hearing and balance• Outer Ear

– consists of the pinna (visible portion of the ear) and the auditory or acoustic canal

– sound waves arrive at the pinna and are directed into the auditory canal

– the canal channels the sound to the eardrum or tympanic membrane which is a partition between the outer and middle ears

The Senses


The Senses

• The Middle Ear is an air filled chamber within the temporal bone and contains 3 bones: the malleus (hammer), incus (anvil) and stapes (stirrup)– when soundwaves strike the eardrum, it causes the

membrane to vibrate. The vibrations cause the malleus, incus and stapes to vibrate also.

– The stapes touches another membrane, called the oval window (the beginning of the inner ear), and causes this membrane to vibrate.

– The Eustachian tube is a connection between the middle ear and throat.

• It acts to equalize air pressure in the middle ear with that of the surrounding atmosphere


The Senses

• So, we have air conduction of sound via the outer ear and this is changed to bone conduction of sound in the middle ear

• Inner Ear– consists of the cochlea (where sound is

converted into fluid movement), the vestibule and 3 semicircular canals

– within the cochlea is the Organ of Corti which contains tactile receptors or hair cells


The Senses

– the hair cells vibrate and bend which releases a neurotransmitter that generates impulses to nearby sensory neurons

– different parts of the organ of Corti respond to different pitched tones so we can hear variations in sounds

• These impulses travel to the auditory nerve and we “hear” the sound


The Senses

• Balance and Equilibrium– the Vestibular Apparatus consists of

• the 3 semicircular canals for sensing rotational movement of the head and body (dynamic equilibrium). This tells us where we are in space.

• the vestibule which senses static (stationary) balance and linear acceleration of the head (static equilibrium)


The Senses

• The vestibule– contains hair cells, gel and otoliths (hard

crystals of bone like material)– when the head tips forward, the otoliths

slide toward the gravitational pull causing the hair cells to bend

– this produces impulses in nearby sensory neurons which are transmitted to the brain for interpretation


REMINDER, Page 1 of 2: 1. Long lab; you can work in groups of 3 if

needed. 2. Perform the receptor tests on page 87 and

88.3. Learn the parts of the eye on the eye

models and the sheep eye. Use the bulleted list on page 91 for parts to identify on both.

4. Remember to follow safety procedures.


REMINDER, Page 2 of 2:5. When finished with the sheep eyes, discard them in

the "discard" bucket.6. Perform the eye tests on pages 90-92. You do not

need to do the color blindness tests.7. Learn the parts of the ear on the ear models. Use

the bulleted list on page 94 to know what structures to locate.

8. Perform the ear tests on page 94. Do not perform the frequency test.

9. Strike the tuning fork on your palm, not on the table. Hold the fork by the bottom peg.