Tuesday, 25 October 2011


The human ear has three main parts – the outer ear, the middle ear and the inner ear.

Outer ear
a) Pinna (ear flap)
b) Ear cannal
Shape like funnel. Made of cartilage and skin.
A 2.5 cm long, narrow tube lined with hair.
Collects and directs sound waves into the ear canal
Directs sound waves to the eardrum
Middle ear
a) Eardrum
b) Ossicles
c) Oval window
d) Eustachian tube
A thin , stretched membrane at the end of the ear canal
Three small bones
A thin , small membrane at the end of the ossicles
A narrow tube that connects the middle ear to the back of the throat.
Vibrates when sound waves hit it
Amplify vibrations and transfer them from the eardrum to the oval window.
Transfers vibrations from the ossicles to the cochlea
Equalises the air pressure on both sides of the eardrum, thus preventing itu from damage.
Inner ear
a) Cochlea
b) Auditory nerve
c) Semicircular canals
A called tube filled with fluid and lined with tiny hair-like sensory cells.
Nerve fibres that connect the ear to the brain
Three semicircular cannals situated at right angles to each other. Contain fluid and sensory cells.
Detects vibrations and converts them into nerve impulses
Carries vibrations and converts them into nerve impulses
Detect the position and movement of the head to help us keep our balance (Note: They are not involved in the hearing mechanism.

 How sounds are detected by the ear :

a)    The pinna collects sound waves and directs them along the ear canal to the eardrum.

b)   When the sound waves hit the eardrum, it vibrates at the same frequency as the sound waves. The vibrations are then transferred to the ossicles.

c)    The ossicles amplify for the vibrations about 20 times before transferring them to the oval window.

d)    The vibration of the oval windows causes the fluid in the cochlea to move in the form of waves . The   
       movement of the fluid stimulates the sensory cells or receptors in the cochlea. Nerve impulses are produced.

e)    The auditory nerve carries the impulses to the brain.

f)    The brain interprets the impulses as sounds.

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