deafness

See deafly.

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Partial or total inability to hear.

In conduction deafness, the passage of sound vibrations through the ear is interrupted. The obstacle may be earwax, a ruptured eardrum, or stapes fixation, which prevents the stapes bone from transmitting sound vibrations to the inner ear. In sensorineural deafness, a defect in the sensory cells of the inner ear (e.g., injury by excessive noise) or in the vestibulocochlear or eighth cranial nerves prevents the transmission of sound impulses to the auditory centre in the brain. Some deaf people are helped by hearing aids or cochlear implants; others can learn to communicate with sign language and/or lip reading.

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      partial or total inability to hear. The two principal types of deafness are conduction deafness and nerve deafness. In conduction deafness, there is interruption of the sound vibrations in their passage from the outer world to the nerve cells in the inner ear. The obstacle may be earwax that blocks the external auditory channel, or stapes fixation, which prevents the stapes (one of the minute bones in the middle ear) from transmitting sound vibrations to the inner ear. In nerve deafness, some defect in the sensory cells of the inner ear (e.g., their injury by excessive noise) or in the vestibulocochlear nerve prevents transmission of sound impulses from the inner ear to the auditory centre in the brain. Deafness at birth is nearly always of the nerve type and cannot be improved by medical means.

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