Fine structure of synapses in the vestibular ganglion of the cat

The vestibular ganglion of cat contains two distinguishable cell types, the larger and myelinated of which are much more numerous. The smaller and unmyelinated are represented by two cell populations: the first population displays complete Schwann cell ensheathment. The sheath of the second population is usually discontinuous at more than one point. Few axosomatic synapses are present on either cell type and profiles with clear synaptic vesicles predominate on each. The populations of presynaptic profiles in general are one type: a large variety with round synaptic vesicles and an asymmetrical contact. This type contacts the cell soma or the axon hillock surface. Those containing myelinated cells are covered on one side by the myelin sheath of the cell soma. Potential origins for the presynaptic profiles and possible functional significance of the synapses is discussed.