Scanning electron microscopy of the nerve endings of Corti's organ.

Scanning electron microscopy (SEM) study of the innervation of the organ of Corti has been carried out for many years. Various methods have been used in attempts to observe more details of the endings of nerve fibers on the sensory hair cells. In this study, a new method of microdissection of Corti's organ was done using a small piece of double-sided adhesive tape. This method is simple and facilitates observation of Corti's organ from the basal to the apical turns. Using it we found variations of the nerve endings and the Deiters' cells in each half turn beginning from the lower basal turn to the upper fourth turn. Nerve endings at the lower poles of outer hair cells are arranged in clusters, and are reduced in size and number as the upper turn is approached. On the contrary, the Deiters' cells are increased in size toward the upper turn, therefore nerve endings in the upper turn are often covered by Deiters' cells. Small nerve endings high on the side of the outer hair cell were also observed. Although there was clear evidence of ultrastructural change in the hair cells' cilia after administration of ototoxic drugs or after hyperstimulation by sound, there was no evidence of concomitant ultrastructural change in the nerve endings. Nerve endings appeared to be more resistant than the hair cells.