The Senses
The Senses
• There are five senses; smell, sight, touch, taste and
hearing.
• Balance is now thought of as a sense.
• Touch detects pressure, pain and hot and cold
substances.
• Our senses are based on receptor cells and nerve
endings, which combine to form the sense organ.
• Receptors respond to heat, light, pressure and
chemicals. They are forms of energy, which are
converted to electrical impulses and produce a message,
which is sent along the neurons.
Sense
Organs
Stimulus
Touch
Skin
Touch &temperature
Taste
Tongue & lining of
throat
Dissolved chemicals
Smell
Nose
Chemicals in gas
state
Sight
Eyes
Light
Hearing
Ears
Sound
Taste
Taste
• Receptors for taste are located in the buds.
• They are found on the top and sides of the
tongue and in the lining of the throat.
• There are four taste receptors; sweet, sour, bitter
and salt.
• Tastes dissolve and lodge in the grooves of the
taste buds where the flavour of the food is a
combination of taste, smell, texture and
temperature
Structure of the Eye
Functions of the parts of the eye.
• Sclera: tough white outer coat that
holds the eye in shape.
• Choroids: dark brown layer, which
contains blood vessels that nourish the
eye and absorbs any light that passes
through the retina thus preventing the
reflection of light within the eye.
Functions of the parts of the eye.
• Retina: light sensitive layer that
contains rod and cone receptors.
• Fovea: located at the centre of the
retina, cones are found here and images
are formed when we look at an object.
Functions of the parts of the eye.
• Optic Nerve: carries impulses from
the eye to the brain.
• Blind Spot: there are no rods or
cones here. We cannot see any images
formed here.
• Cornea: transparent section of the eye
that allows light in.
Functions of the parts of the eye.
• Lens: changes shape to focus light on
the retina.
• Ciliary Muscle: changes the shape
of the lens.
• Iris: coloured part of the eye, which
controls the amount of light entering the
eye.
The Pupil
The Pupil
• The pupil is the black circle in the centre of
the eye, which allows light into the eye.
• In dim light, the size of the pupil enlarges
or dilates to allow more light to enter the
eye.
Aqueous and vitreous humours
• The aqueous and vitreous humours are
liquids that support the eye while the
external muscles allow movement.
Rods and Cones
Rods
Cones
Shape
Rod shaped
Cone shaped
Detect
Black & white light
Colours
Active in
Dim light
Bright light
Location
All over the retina
At the fovea
120 million
6 million
No. per eye
Rods and Cones
• The pigment in the rods is called
rhodopsin, which is formed from vitamin A.
• The cones have three pigments, red,
green and blue light.
The Ear
Functions of the parts of the
ears.
• The functions of the ear are hearing and
balance.
• The ear is composed of three sections, the
outer, middle and inner ear.
• The outer and middle ear is filled with air
and the inner ear is filled with fluid called
lymph
Functions of the parts of the
ears.
• Sound is caused by vibrations in the air,
which are collected by the outer ear,
passed through the middle ear where they
are amplified and transferred to fluid lymph
in the cochlea of the inner ear.
• The cochlea is stimulated by pressure
waves in the lymph, which sends electrical
impulses to the brain, which in turn
interprets them.
The Outer Ear (Air).
• The pinna is made of cartilage, which
collects vibrations in the air and channels
them into the ear.
• The auditory canal carries vibrations to
the eardrum.
• The eardrum is a tightly stretched
membrane that vibrated when stimulated
by vibrations in the auditory canal.
The Middle Ear (Air)
The Middle Ear (Air)
• The ossicles are three bones, the
hammer, anvil and stirrup.
(The stirrup is the smallest bone in the
body, which increases the vibrations and
pass them on to the oval window).
• The Eustachian tube connects the middle
ear to the throat.
(It equalises pressure on either side of the
eardrum).
The Inner Ear
(Diagram not on course)
The Inner Ear (Lymph Fluid).
• The cochlea is a spiral tube, which allows
hearing. Vibrations hit the lymph in the
cochlea through the oval window. As the
vibrations pass through the window they
stimulate the pressure receptors in the
cochlea. Impulses are sent along the
receptors to the cerebrum along the
auditory canal.
The Semi-Circular Canals
The Semi-Circular Canals
• The three semi circular canals are at
right angles to each other and form part of
the vestibular apparatus.
• The function of the semi circular canals is
balance. Receptors in the canals detect
when our head is moving or rotating. The
receptors send impulses to the cerebrum
of the brain through the vestibular nerve.
Glue Ear - A hearing disorder.
Cause
• Glue ear is caused by too much fluid
collecting in the middle of the ear in young
children.
• The build up of fluid is often the result of a
viral infection
Glue Ear - A hearing disorder.
Syptoms
• Can cause loss of hearing as it prevents
the three bones in the middle ear from
moving properly.
Glue Ear - A hearing disorder.
Corrective measures
• Decongestant drugs are taken which
break up the fluid and allow drainage of
the fluid through the Eustachian tubes.
• In severe cases grommets are placed in
the eardrums, which allow air to enter the
middle ear and force the fluid down
through the Eustachian tubes.