Types of Deafness

Deafness is usually divided into two types: (1) that caused by impairment of the cochlea or impairment of the auditory nerve, which is usually classified as "nerve deafness," and (2) that caused by impairment of the physical structures of the ear that conduct sound itself to the cochlea, which is usually called "conduction deafness."

If either the cochlea or the auditory nerve is destroyed, the person becomes permanently deaf. However, if the cochlea and nerve are still intact but the tympanum-ossicular system has been destroyed or ankylosed ("frozen" in place by fibrosis or calcification), sound waves can still be conducted into the cochlea by means of bone conduction from a sound generator applied to the skull over the ear.

Audiometer. To determine the nature of hearing disabilities, the "audiometer" is used. Simply an earphone

Figure 52-13

Audiogram of the old-age type of nerve deafness.

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Essentials of Human Physiology

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