Sensory hair cells of vertebrates convert mechanical energy into electrical signals for transmission to the central nervous system.Most hair cells also are postsynaptic to efferent neurons that project from the central nervous system to inhibit peripheral function.Calcium ions are essential cytoplasmic mediators of both afferent and efferent synaptic function.However,like other so-called ‘short receptors (taste cells,photoreceptors) hair cells are physically compact,possessing neither axons nor dendrites to provide spatially-segregated calcium signals for separate synaptic processes.