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The Mechanics of Hearing
and Hearing Loss

Courtesy of the
Hearing Foundation of Canada

Sound waves in the air are directed by the outer ear into the ear drum causing it to vibrate very slightly. The three bones of the middle ear (the smallest bones in the human body) work together as a lever system to amplify the vibrations as they pass them along to a smaller vibrating membrane on the surface of the cochlea of the inner ear. This vibration is passed on by the fluid filled spiral tube of the cochlea to tiny hair cells along the inside. As the hairs move, nerve cells at their base change this motion into electrical signals that are passed on to the brain. The brain in turn interprets those signals as sound.

Hearing loss or impairment can stem from a variety of problems, which can occur as sound is transferred along this mechanical and electrical paths to the brain. The causes can be as simple (and reversible) as wax build up or inflammation of the outer ear, or more serious yet often self-repairing broken eardrum, or even abnormal or dislocated bones of the middle ear.

Inner ear damage can be acquired from a short blast or repeated or prolonged exposure to loud noise (construction noise or a Walkman cranked up too loud). The delicate hairs in the cochlea can be irreparably destroyed. High frequency sounds are usually the first to go. Disease, infection or drugs can also damage the inner ear.

Hearing loss can also exist at birth. Hereditary abnormalities or other numerous syndromes may cause a delayed onset of hearing loss. Damage may have been acquired in birth trauma or as a result of prenatal infection or drug use.

Hearing loss at birth can severely handicap language development. In childhood it can cause language delay and learning problems. Acquired in adulthood there remains social and occupational handicaps as well as loss of pleasure of music or conversation.

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