Sense of Hearing

 

The Ear

1. The ears are the sensory organs of hearing.
They are sensitive
to sound.

 

2. The human ear is made up of the outer ear, the middle ear and the inner ear.

 

3. The outer ear and middle ear are filled with air. Only the inner ear is filled with fluid.

 

The structure and function of each part of the human ear:

 

 

Part

Structure

Function

Outer Ear

Pinna

Shaped like a funnel. Made of cartilage and skin.

Collects and directs sound waves into the ear canal.

Ear/auditory canal

A 2.5 cm long, narrow tube lined with hair

Directs sound waves to the eardrum.

Middle Ear

Eardrum

A thin, stretched membrane at the end of the ear canal.

Vibrates when sound waves hit it. Thus, it changes sound energy to kinetic energy.

Ossicles

Three small bones that connect the eardrum and oval window.

Amplify vibrations and transfer them from the eardrum to the oval window.

Oval window

A thin, small membrane at the end of the ossicles

Transfers vibrations from the ossicles to the cochlea.

Eustachian tube

A narrow tube that connects the middle ear to the back of the throat.

Equalizes the air pressure on both sides of the eardrum, thus preventing it from damage.

Inner Ear

Cochlea

A coiled tube filled with fluid and lined with hair-like sensory cells.

Detects vibrations and converts them to nerve impulses. Thus, it changes kinetic energy to electrical energy.

Auditory nerve

Nerve fibres that connect the ear to the brain.

Carries nerve impulses from the cochlea to the brain.

Semi-circular canals

Three semi-circular tubes situated at right angles to each other. Contain fluid and sensory cells.

Detect the position of the head to help us keep our balance. Not involved in the hearing mechanism.

 

 

The Hearing Mechanism

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

 

2. When the sound waves hit the eardrum, it vibrates at the same frequency as the sound waves.

 

3. The vibrations are them transferred to the ossicles. The ossicles amplify the vibrations about 20 times before transferring them to the oval window.

 

4. The vibration of the oval window causes the fluid in the cochlea to move in the form of waves. This movement of the fluid stimulates the sensory cells (receptors) in the cochlea. Nerve impulses are produced.

 

5. The auditory nerve carries the impulses to the brain. The brain interprets the impulses as sound.