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The Senses
Reception of stimuli
Contents
The Senses & Organs
Classification of the
senses
Interoceptors
Exteroceptors
How they work
Taste and Smell –
smell
Taste and Smell - taste
Touch
Ear
Hearing
Hearing defects
Balance
Vision
Eye – Parts &
function
Eye defects
Visual disorders
2
The Senses & Organs
Sense
Organ
Taste
Smell
Touch
Hearing
Sight
Balance
Pressure
3
Classification of the
senses
Classified according to type of stimulus to
which they respond.
Two groups –
Interoceptors
and
Exteroceptors
4
Interoceptors
interoceptors: sensory receptors that
respond to changes in the internal
environment, e.g. stretch receptors in
the muscles.
5
Exteroceptors
exteroceptors: sensory receptors that
respond to external changes in the
environment, e.g. taste receptors.
6
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 work
The 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 - smell
Closely 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 human smell
receptors
What happens to
your sense of
smell when you
have a cold?
Why?
10
Taste and Smell - taste
Taste 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 human taste
receptors
Tongue, rabbit, showing
taste buds
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Touch
Found in the skin.
Involves the ability to sense a number of
stimuli e.g.
Touch receptors – gentle force on hairless
skin – palm of hand
Pressure receptors – greater force –
found all over the body
Pain receptors – found over the whole
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skin.
Various sense
receptors in the skin
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Skin of
the scalp
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Skin, hair
follicle,
sebaceous
gland
17
Skin, sweat glands
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Ear
Divided into three sections: -
Outer
Middle
Inner
- Air filled
- Air filled
- Fluid filled
- up to eardrum
- to oval window
- cochlea
19
Hearing
(1/3)
hearing: perception by the brain of the
action of sound on the eardrum.
Sound picked up by pinna
Funnelled into ear canal
Strikes off eardrum (tympanum)
Eardrum vibrates
Pressure on both sides of the eardrum is
kept the same by the Eustachian tube
This connects the middle ear to the throat.
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The human ear
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 human ear
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 ear
e.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 semicircular canals.
Fluid filled structures that detect
movement and position of the head.
They are used to keep you balanced.
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Vision
vision: 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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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
LONG
SIGHT
SHORT
SIGHT
MEDICAL
TERM
DIAGNOSIS
DEFECT
SOLVE BY
WEARING
Cannot
Eyeball
HypermConvex
see near
too
etropia
lenses
objects
short
Cannot
Eyeball Concave
Myopia see distant
too long lenses
objects
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Visual disorders
Not examinable
for information only
Visual problems
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Glaucoma
42
END
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