Figure 4. End bulb ultrastructure.

Large auditory nerve terminals, or endbulbs, ensheathed in glial processes (glia) contact bushy cell bodies (CB) in both rostral AVCN and caudal AVCN (A–E). These terminals contain mitochondria clusters (mit) and many LR SVs associated with curved, asymmetric PSDs (single asterisks). Mitochondrial adherens complexes (MAC), puncta adherentia (puncta), and intermembranous cisternae (cis) are often observed. Endbulbs sometimes form synapses (double asterisks) with nearby dendritic processes (d) presumed to originate from nearby bushy cells. Occasionally, very large endbulbs are observed in proximity to numerous dendritic processes (E). Multiple release sites are common (A–D), but are not always separated by intermembranous cisternae (A, E).