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 babys 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 depends on the intensity and duration of the noise.
The effects may be temporary or permanent. A single exposure to an extremely intense sound, such as an explosion, may produce a severe and permanent loss of hearing. Repeated exposures to sounds in excess of 80 to 90 decibels may cause gradual deterioration of hearing by destroying the hair cells of the inner ear, with possible subsequent degeneration of nerve fibers. The level of noise produced by rock music bands usually exceeds 110 decibels. The noise generated by farm tractors, power mowers, and snowmobiles may reach 100 decibels. In the United States, legislation requires that workers exposed to sound levels greater than 90 decibels for an eight-hour day be provided some form of protection, such as earplugs or earmuffs.
Individuals differ in their susceptibility to hearing loss from noise exposure; because hearing loss typically begins at the higher frequencies of 4,000 to 6,000 hertz, the effects of noise exposure may go unnoticed until the hearing loss spreads to the lower frequencies of 1,000 to 2,000 hertz. Inhalation of carbogen, a mixture of 5 percent carbon dioxide and 95 percent oxygen for twenty minutes will accelerate recovery of hearing if administered within a few hours after excessive noise exposure. (Lucente 90) Labyrinthitis is the inflammation of the labyrinth of the inner ear. This is caused by infections such as meningitis, syphilis, acute otitis media and mastoiditis, or chronic otitis media and cholesteatoma(A complication of chronic otitis media). (Infomedical) Cholesteatoma can create negative pressure in the middle ear such that a mass consisting of keratin and epidermis is drawn into the middle ear through a perforated eardrum.
Cholesteatoma typically erodes the mastoid bone and causes damage the ossicles (three small bones of the middle ear). (Infomercial) Loss of both equilibrium and hearing occurs in the affected ear. Prompt antibiotic treatment sometimes arrests the damage and allows for the possibility of partial recovery of the function of the inner ear.(Infomedical) An acoustic …
