The ear is made up of the outer, middle and inner ear. The outer earconsists of the auricle, the external auditory canal and the lobe. The outer earhelps to funnel sound and noise into the middle ear. The middle ear consists ofthe 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 wheresound is interpreted through electrical impulses relayed to brain intounderstandable sounds that we recognize.
(Lucente3-8) The labyrinth of the innerear contains the nerve endings of the vestibular nerve–the nerve ofequilibrium-and the auditory nerve, which are branches of the vestibulocochlear,or eighth cranial, nerve. The vestibular nerve ends supply the semicircularcanals and the otolithic membranes in the vestibule. The auditory nerve suppliesthe cochlea. Diseases of the labyrinth of the inner ear may affect both thevestibular nerve and the auditory nerve, or they may affect only the auditorynerve, with loss of hearing. (Lucente 6) The most common causes of inner-eardiseases are congenital nerve deafness, viral infections, and ototoxic drugs.
Congenital nerve deafness is a defect of the auditory nerve in the cochlea andmay be present at birth or acquired during or soon after birth. Usually bothinner ears are affected to a similar degree, and there is a severe impairment ofhearing, although in some cases of congenital nerve loss the impairment can bemoderate. Many cases of congenital nerve deafness have been caused by therubella (German measles) virus in the mother during the first three months ofher pregnancy. This can happen during a rubella epidemic, even when the motherhas no symptoms of the infection. In most cases the vestibular nerve is notaffected or is affected to a lesser degree, and in most (but not all) cases theouter and middle ear structures are not affected.
A vaccine against the rubellavirus made available in 1969 has reduced the number of cases of congenital nervedeafness in developed countries. (Lucente 84-87) Congenital nerve deafnessacquired at or soon after birth may result from insufficient oxygen (anoxia)during a difficult and prolonged delivery or from incompatibility between thebabys blood and that of its mother. In a few cases congenital nerve deafnessis an inherited failure of the cochlea to develop properly. When the hearingloss is severe, speech cannot be acquired without special training.
Childrenafflicted with hearing loss must attend special classes or schools for theseverely deaf, where they can be taught lip-reading, speech, and sign language. Electrical hearing aids can be helpful, especially during classes, to use theresidual hearing. Another alternative, although controversial within the deafcommunity, is a cochlear implant, which is sometimes useful in cases of profoundhearing loss. In this operation, an electrode is surgically implanted in the earto 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 oneear, and sometimes in both, at any age. The Mumps virus is one of the mostcommon causes of severe sensorineural hearing loss in one ear. The measles andinfluenza viruses are less common.
There is no effective medical or surgicaltreatment to restore hearing impaired by a virus. (Lucente 95) Ototoxic (harmfulto the ear) drugs can cause temporary and sometimes permanent impairment ofauditory nerve functions. Certain drugs like aspirin in large enough doses maycause ringing in the ears and then a temporary decrease in hearing that ceaseswhen the person stops taking the drug. Quinine can have a similar effect but maycause permanent impairment of auditory nerve functions in some cases. Certainantibiotics, such as streptomycin and neomycin may cause permanent damage toauditory nerve functions. Susceptibility to auditory nerve damage from ototoxicdrugs varies greatly among individuals.
In most cases, the vestibular nerve isnot affected. Streptomycin affects the vestibular nerve more than it affects theauditory nerve. (Lucente 89) Skull fractures and concussions from a severe blowon or to the head can impair the functioning of the auditory and vestibularnerves in varying degrees. The greatest hearing loss arises when a fracture ofthe skull passes through the labyrinth of the inner