Chemical Neuroanatomy in the Vestibular System

Vestibular neurons in the internal auditory canal are composed of afferent and efferent fibers. Vestibular primary afferent neurons have their cell somata, so-called Scarpa's ganglion cells, localized in the canal. Vestibular afferents receive afferent signals from vestibular hair cells and transmit them to vestibular nuclei and vestibulocerebellum. Vestibular afferents also receive efferent signals via axo-dendritic synapses between calyxes and vestibular efferent fibers. According to the afferent and efferent information, vestibular afferents have crucial bipolar effects both on distal and proximal synapses. In this review article, I would like to discuss the roles of vestibular neurons, including both afferents and efferents, in terms of neurotransmitters and neuromodulators.