The Afferent Synapse of Cochlear Hair Cells

Mechanosensory hair cells of the cochlea must serve as both transducers and presynaptic terminals, precisely releasing neurotransmitter to encode acoustic signals for the postsynaptic afferent neuron. Remarkably, each inner hair cell serves as the sole input for 10-30 individual afferent neurons, which requires extraordinary precision and reliability from the synaptic ribbons that marshal vesicular release onto each afferent. Recent studies of hair cell membrane capacitance and postsynaptic currents suggest that the synaptic ribbon may operate by simultaneous multi-vesicular release. This mechanism could serve to ensure the accurate timing of transmission, and further challenges our understanding of this synaptic nano-machine.