Hearing Loss

Being deaf is a handicap that afflicts millions of people around the world every
year. Hearing loss can result from any number of afflictions that can affect the
outer, middle, or inner ear. The range of hearing loss can also vary from mild
to severe. The ear is made up of the outer, middle and inner ear. The outer ear
consists of the auricle, the external auditory canal and the lobe. The outer ear
helps to funnel sound and noise into the middle ear. The middle ear consists of
the eardrum and the three middle ear bones, the Mallues, Incus, and the Stapes.

The middle ears primary function is to conduct sound. The inner ear is where
sound is interpreted through electrical impulses relayed to brain into
understandable sounds that we recognize. (Lucente3-8) The labyrinth of the inner
ear contains the nerve endings of the vestibular nerve--the nerve of
equilibrium-and the auditory nerve, which are branches of the vestibulocochlear,
or eighth cranial, nerve. The vestibular nerve ends supply the semicircular
canals and the otolithic membranes in the vestibule. The auditory nerve supplies
the cochlea. Diseases of the labyrinth of the inner ear may affect both the
vestibular nerve and the auditory nerve, or they may affect only the auditory
nerve, with loss of hearing. (Lucente 6) The most common causes of inner-ear
diseases are congenital nerve deafness, viral infections, and ototoxic drugs.

Congenital nerve deafness is a defect of the auditory nerve in the cochlea and
may be present at birth or acquired during or soon after birth. Usually both
inner ears are affected to a similar degree, and there is a severe impairment of
hearing, although in some cases of congenital nerve loss the impairment can be
moderate. Many cases of congenital nerve deafness have been caused by the
rubella (German measles) virus in the mother during the first three months of
her pregnancy. This can happen during a rubella epidemic, even when the mother
has no symptoms of the infection. In most cases the vestibular nerve is not
affected or is affected to a lesser degree, and in most (but not all) cases the
outer and middle ear structures are not affected. A vaccine against the rubella
virus made available in 1969 has reduced the number of cases of congenital nerve
deafness in developed countries. (Lucente 84-87) Congenital nerve deafness
acquired at or soon after birth may result from insufficient oxygen (anoxia)
during a difficult and prolonged delivery or from incompatibility between the
baby's blood and that of its mother. In a few cases congenital nerve deafness
is an inherited failure of the cochlea to develop properly. When the hearing
loss is severe, speech cannot be acquired without special training. Children
afflicted with hearing loss must attend special classes or schools for the
severely deaf, where they can be taught lip-reading, speech, and sign language.

Electrical hearing aids can be helpful, especially during classes, to use the
residual hearing. Another alternative, although controversial within the deaf
community, is a cochlear implant, which is sometimes useful in cases of profound
hearing loss. In this operation, an electrode is surgically implanted in the ear
to directly stimulate the auditory nerve between the brain and the ear. (www.deaf.com)

Viral infections can cause severe degrees of sensorineural hearing loss in one
ear, and sometimes in both, at any age. The Mumps virus is one of the most
common causes of severe sensorineural hearing loss in one ear. The measles and
influenza viruses are less common. There is no effective medical or surgical
treatment to restore hearing impaired by a virus. (Lucente 95) Ototoxic (harmful
to the ear) drugs can cause temporary and sometimes permanent impairment of
auditory nerve functions. Certain drugs like aspirin in large enough doses may
cause ringing in the ears and then a temporary decrease in hearing that ceases
when the person stops taking the drug. Quinine can have a similar effect but may
cause permanent impairment of auditory nerve functions in some cases. Certain
antibiotics, such as streptomycin and neomycin may cause permanent damage to
auditory nerve functions. Susceptibility to auditory nerve damage from ototoxic
drugs varies greatly among individuals. In most cases, the vestibular nerve is
not affected. Streptomycin affects the vestibular nerve more than it affects the
auditory nerve. (Lucente 89) Skull fractures and concussions from a severe blow
on or to the head can impair the functioning of the auditory and vestibular
nerves in varying degrees. The greatest hearing loss arises when a fracture of
the skull passes through the labyrinth of the inner ear, totally destroying its
function. The effect of noise exposure on one's hearing