Bma Illustrated Medical Dictionary

earThe organ of hearingand balance. It

consists of three parts: the outer ear,

the middle ear, and the inner ear.

The outer ear comprises the pinnaand

the ear canal. The outer part of the ear

canal produces earwax, which traps

dust and foreign bodies. The canal is

closed at its inner end by the eardrum,

which vibrates in response to changes

in air pressure that make sound.

The middle ear is a cavity that con-

ducts sound to the inner ear by means

of three tiny, linked, movable bones

known as ossicles. The first bone, the

malleus, is joined to the inner surface

of the eardrum. The second, the incus,

is linked to the malleus and to the third

bone, the stapes. The base of the stapes

fills the oval window leading to the

inner ear. The eustachian tubelinks the

middle ear to the back of the nose.

The inner ear is an intricate series of

structures deep within the skull. The

front part, the cochlea, is a tube con-

taining nerve fibres that detect different

sound frequencies. The rear part of the

inner ear contains three semicircular

canals and is concerned with balance.

The semicircular canals are connected

to a cavity called the vestibuleand con-

tain hair cells bathed in fluid. Some of

these cells are sensitive to gravity and

acceleration; others detect direction of

movement. Information from the inner

ear is conducted to the brain via the

vestibulocochlear nerve.

earachePain in the ear. Earache is a

common symptom, especially in child-

hood. The most frequent cause is acute

otitis media, which results in severe,

stabbing pain. Another common cause

of earache is otitis externa. The pain may

be accompanied by irritation and a dis-

charge of pus. Intermittent earache may

accompany dental problems, tonsillitis,

throat cancer (see pharynx, cancer of),

or pain in the jaw or neck muscles.

EAR EARACHE

E

Cartilage

Vestibulo-

cochlear

nerve

Muscle

Cochlea

Malleus

Incus

Stapes

Semicircular

canals

Eustachian

tube

Eardrum

Ear canal

Pinna

Oval

window

EAR

Skull

bone

Cut edge

of cochlea

Outer

ear

Middle ear Inner ear

PARTS OF EAR

E