Synaptogenesis of the efferent vestibular nerve endings of the cat: ultrastructural study.

The maturation of the innervation of the sensory hair cells of the cristae ampullares was studied in the newborn cat. The essential characteristics of the adult are already present in the type II cells at this age. The type I cells on the contrary reveal different degrees of maturation. It was observed that in the immature stages the efferent endings which were already filled with synaptic vesicles were in direct contact with the membrane of the sensory cell. The nerve chalice as it settles into place breaks this contact and simultaneously a synapse is created between the efferent endings and the afferent chalice.