Synaptic Dynamics

The concentrations of two calcium buffers (left) and the synaptic resonant frequency (center) rise with declining distance from one end of the auditory organ. A mathematical model (right) explains why the calcium-buffer concentrations increase with the synaptic resonant frequency. The black line demarcates the physiological range.

  • Deflection of a hair bundle arising from a sensory stimulus depolarizes its hair cell triggering neurotransmitter release at the cell’s ribbon synapse. The dynamics of synaptic release impact how inner-ear vibrations are translated into afferent action potentials.
  • In some organs, neurotransmitter release peaks as a function of the stimulus frequency, which may improve the system’s frequency tuning. The resonant frequency of synaptic release was observed to be correlated with the concentration of calcium buffers in hair cells1. Mathematical modeling explains how tonotopic gradients in calcium-buffer concentrations leads to systematic changes in the synaptic resonant frequency with location (see figure). How receptor-potential and synaptic dynamics filter sensory input to determine the inner ear’s output are subjects of current interest.