Retrograde degeneration of the cochlear nerve.

Retrograde degeneration of the cochlear neurons has been studied in different types and degrees of peripheral cochlear damage such as acoustic trauma, intoxication, heredodegenerative deafness and others. It starts only when the peripheral dendrites to the inner hair cells are irreversibly damaged. About 10% of the neurons are not affected by retrograde degeneration. They correspond to the type II and III neurons, which also survive after transection of the cochlear nerve and are mainly associated with the outer hair cells. Cochlear damage due to vascular impairment usually leads to a complete loss of cochlear neurons. In hereditary abiotrophic deafness, neuronal degeneration is slower and its extent varies considerably according to the various genetic syndromes.