Innervation Densities of the Cochlea

Abstract

In normal cats the nerve fibres have been counted at different levels from the spiral ganglion to the outer hair cells by means of light and electron microscopy. The relative numbers were calculated per millimeter cochlear length. Thus more exact information has been obtained about the ratio of the nerve supply to the inner and outer hair cells, the innervation density and the fibre branching in different cochlear turns. The great predominance of the innervation of the inner hair cells is confirmed. Only a small proportion of all nerve fibres leads to the outer hair cells. There is an overall innervation density maximum in the upper basal turn. About 95% of the afferent cochlear neurons are associated with the inner hair cells and only about 5% with the outer hair cells. The neurons associated with the outer hair cells have entirely different structural characteristics and do not undergo retrograde degeneration.