Depolarization of the hair cell causes the release of a neurotransmitter at its basal surface and the initiation of nerve impulses in a sensory neuron that synapses with it. Detection of a given frequency is a function of the location of the hair cells along the organ of Corti with the highest frequencies detected near the base of the cochlea and the remainder of the sound spectrum detected in a progressive fashion with the lowest frequencies detected by hair cells near the tip. Deafness Deafness may be acquired or inherited. If a laboratory animal is exposed to very intense, pure tones, it eventually becomes deaf to those frequencies, but its ability to hear other pitches is unimpaired. Examination of its organ of Corti reveals destroyed hair cells in a single area whose location can be easily correlated with the pitch of the destructive sound.
Similar deficits occur in humans who are exposed to intense noises for long periods.
Inherited deafness About 1 newborn in a thousand is born deaf because of a genetic defect. Literally scores of genes have been identified in recent years whose mutant versions result in hearing loss. The potassium that enters the hair cells must be removed from them and recycled back to the endolymph for hearing to continue. Scores of mutations in the necessary transport molecules have been linked to inherited deafness. Link to a discussion of gap junctions and connexins.