Skip to main content
-
Receptors for touch, pressure, pain and temperature are found in the skin. Receptors in the muscles, tendons and joints inform the brain of limb position.
-
The
olfactory organ
in the nose responds to chemicals in the air i.e. smell.
-
Taste buds
on the tongue respond to a limited range of chemicals dissolved in saliva.
-
The eyes are the organs of sight. Spherical
eyeballs
situated in orbits in the skull have walls composed of 3 layers.
-
The tough outer
sclera
protects and holds the shape of the eyeball. At the front it becomes visible as the white of the eye and the transparent
cornea
that allows light to enter the eye.
-
The middle layer is the
choroid
. It most animals it absorbs stray light rays but in nocturnal animal it is reflective to conserve light. At the front of the eye it becomes the
iris
with muscles to control the size of the
pupil
and hence the amount of light entering the eye.
-
The inner layer is the
retina
containing the light receptor cells: the
rods
for black and white vision in dim light and the
cones
for colour and detailed vision. Nerve impulses generated by these cells leave the eye for the brain via the
optic nerve
.
-
The
lens
(with the cornea) helps focus the light rays on the retina. Muscles alter the shape of the lens to allow near and far objects to be focussed.
-
Aqueous humour
fills the space immediately behind the cornea and keeps it in shape and
vitreous humour
, a transparent jelly-like substance, fills the space behind the lens allowing light rays to pass through to the retina.
-
The ear is the organ of hearing and balance.
-
The external
pinna
helps funnel sound waves into the ear and locate the direction of the sound. The sound waves travel down the external
ear canal
to the
eardrum
or
tympanic membrane
causing it to vibrate. This vibration is transferred to the
auditory ossicles
of the middle ear which themselves transfer it to the inner ear. Here receptors in the
cochlea
respond by generating nerve impulses that travel to the brain via the
auditory
(acoustic) nerve.
-
The
Eustachian tube
connects the middle ear with the pharynx to equalise air pressure on either side of the tympanic membrane.
-
The
vestibular organ
of the inner ear is concerned with maintaining balance and posture. It consists of the
semicircular canals
and the
otolith organs
.