The Senses

Reception of stimuli

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ContentsThe Senses & OrgansClassification of the sensesInteroceptorsExteroceptorsHow they workTaste and Smell – smellTaste and Smell - taste

TouchEarHearingHearing defectsBalanceVisionEye – Parts & functionEye defectsVisual disorders

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The Senses & OrgansSense OrganTaste

Smell

Touch

Hearing

Sight

Balance

Pressure

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Classification of the senses

Classified according to type of stimulus to which they respond.

Two groups –Interoceptors

andExteroceptors

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Interoceptorsinteroceptors: sensory receptors that

respond to changes in the internal environment, e.g. stretch receptors in the muscles.

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Exteroceptorsexteroceptors: sensory receptors that

respond to external changes in the environment, e.g. taste receptors.

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Further division of receptors

Type of Receptor Responds to …

Chemoreceptor Chemicals e.g. taste

Photoreceptors Light e.g. rods & cones

Mechanoreceptors Physical change e.g. pressure

Thermoreceptors Temperature change

Proprioreceptors Movement of the body & position

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How they workThe sense organs contain receptors which

receive the stimuli and send messages to the brain along

sensory neurons. The brain acts as the interpreting centre for

received information.All nervous messages are the same.How they are interpreted by the various

parts of the brain is different.

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Taste and Smell - smellClosely related senses – chemoreceptors.

Chemicals enter the nose and stimulate the olfactory membranes in the back of the nose.

Different chemicals stimulate different receptors resulting in different “smells”.

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The

hum

an sm

ell

rece

ptor

s

What happens to your sense of

smell when you have a cold?

Why?

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Taste and Smell - tasteTaste buds in the tongue are similar.

They respond to chemicals dissolved in the mouth.

Sweet, sour bitter and salt – four basic tastes on different parts of the tongue.

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The

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an ta

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Tongue, rabbit, showing taste buds

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TouchFound in the skin.Involves the ability to sense a number of

stimuli e.g.Touch receptors – gentle force on hairless

skin – palm of handPressure receptors – greater force – found

all over the bodyPain receptors – found over the whole

skin.

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Vario

us se

nse

rece

ptor

s in

the

skin

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Skin of the scalp

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Skin, hair follicle,

sebaceous gland

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Skin, sweat glands

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EarDivided into three sections: -

Outer - Air filled - up to eardrumMiddle - Air filled - to oval windowInner - Fluid filled - cochlea

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Hearing (1/3)

hearing: perception by the brain of the action of sound on the eardrum.

Sound picked up by pinnaFunnelled into ear canalStrikes off eardrum (tympanum)Eardrum vibratesPressure on both sides of the eardrum is

kept the same by the Eustachian tubeThis connects the middle ear to the throat.

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The

hum

an e

ar

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Hearing (2/3)

This is why your ears ‘pop’ with sudden pressure changes e.g. airplane take off.

Vibration of eardrum passed on to the ear ossicles and amplified twentyfold by them (hammer, anvil, stirrup).

Stirrup connected to oval window which leads into the cochlea – a coiled fluid filled tube.

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The

hum

an e

ar

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Hearing (3/3)

In the cochlea the vibrations are converted into nerve impulses and transmitted along the auditory nerve to the brain where they are interpreted as sound.

The vibrations pass along the cochlea and are lost back to the middle ear at the round window.

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Hearing defects (1/2)

Usually caused by damage to the receptors in the cochlea.Continuous loud noise – pneumatic drills, rock concerts, listening to loud musin on earphones.Sudden very loud noise (gunshot)Some loss of receptors occurs with age

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Hearing defects (2/2)

Problems with outer or middle eare.g. glue ear in young children (usually of

smokers) – sticky fluid in middle ear – inserting drainage tubes into ear usually cures this.

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Balance A function of the inner ear – the semi-

circular canals.Fluid filled structures that detect

movement and position of the head.They are used to keep you balanced.

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Visionvision: the sensation resulting from the

stimulation of the light receptors in the eye that allows the shape and colour of an object to be perceived – the sense of seeing, sight.

The eye contains photoreceptors.

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A section through the eye

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Whole

eye,

mammali

an

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Parts and function (1/6)

Eyebrow – directs sweat away from eye.

Eyelid – blink - keep eye clear and moist.

Eyelashes – trap dust and dirt.

Conjunctiva – transparent membrane covering front of eye.

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Parts and function (2/6)

Lacrimal glands – produce tears - wash away dust and bacteria.

Sclerotic coat (sclera) – maintains eyeball shape, strong, opaque and provides muscle attachment.

 Cornea – transparent part of sclera -

allows light to enter eye.

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Parts and function (3/6)

Choroid – dark in colour - prevents light reflection in the eye - contains blood vessels.

Retina – light sensitive layer, contains Rods (dim light) and Cones (colour vision).

 Ciliary body – contains muscles, which

alter the shape of the lens.

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Parts and function (4/6)

Lens – transparent - biconvex - focus light on retina.

Suspensory ligament Attaches ciliary body to lens - helps control / adjust shape of lens

 Iris – coloured part of eye - controls the

amount of light entering the eye.

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Parts and function (5/6)

Pupil – hole in centre of Iris through which light enters eye.

Aqueous humour – clear liquid found between lens and cornea - maintains eyeball shape.

 Vitreous humour – jelly like substance

found between lens and retina - maintains eyeball shape.

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Parts and function (6/6)

Optic nerve – transmits messages from eye to brain.

 Blind spot – where optic nerve leaves

eye - no rods or cones on retina => no vision at this spot.

 Fovea – area of most acute vision on

retina - directly behind centre of lens.

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Eye defects

COMMON NAME

MEDICAL TERM DIAGNOSIS DEFECT SOLVE BY

WEARING

LONG SIGHT

Hyperm-etropia

Cannot see near objects

Eyeball too

short

Convex lenses

SHORT SIGHT Myopia

Cannot see distant

objects

Eyeball too long

Concave lenses

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Long-s

ighted

ness

and i

ts cor

rectio

n

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Short

-sighte

dness

and i

ts cor

rectio

n

Visual disorders

Not examinablefor information only

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Visual problems

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Glaucoma

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END