Understanding Deafness
THE EAR
The ear is an organ of hearing and equilibrium. The human ear consists of outer, middle, and inner parts. The outer ear, the visible portion, includes the skin-covered flap of cartilage (auricle) and the auditory canal, which leads to the eardrum. The middle ear contains three small bones, or ossicles, known because of their shapes as the hammer, anvil, and stirrup. The Eustachian tube connects the middle ear to the throat. The inner ear contains the cochlea, which houses the sound-analyzing cells, and the vestibule, with the organs of balance. In the course of hearing, sound waves enter the auditory canal and strike the eardrum, causing it to vibrate. The waves are concentrated as they pass through the ossicles to a small opening leading to the inner ear. The vibration sets in motion fluid within the cochlea. This agitates a delicate membrane, stimulating thousands of sensory hair cells, which in turn stimulate the auditory nerve to send impulses to the brain. Three fluid-filled semicircular canals and two saclike organs, the utriculus and the sacculus, are the chief organs of balance and orientation; as with hearing, stimulation of sensory hair cells in these organs stimulates nerve impulses.
DEAFNESS
Deafness partial or total loss of hearing. It may be present at birth (congenital) or acquired any time thereafter. Conductive deafness, one of the two major types of deafness, involves a disturbance in the transmission of sound to the nerve receptors of the inner ear. This type of deafness may be caused by infection, impacted wax, perforation of the eardrum, or otosclerosis, a chronic condition, especially in older people, that restricts the vibration of the bone leading to the inner ear. These conditions can usually be treated with ANTIBIOTICS, surgery, hearing aids, and other techniques. The other major type of deafness-perceptive, or nerve, deafness-involves damage to neural receptors in the inner ear, to nerve pathways to the brain, or to the area of the brain concerned with hearing. Usually permanent, it can be caused by infection, senility, tumors, or excessive noise, or it may be congenital. A cochlear implant, in which a tiny receiver is connected by a wire to the inner ear, can sometimes alleviate perceptive deafness. Those who cannot be helped to hear may communicate through SIGN LANGUAGE and lip reading. The first U.S. public school for the deaf was founded in 1817 by T.H. GALLAUDET.
|
