Figure 3.

Electrophysiological responses of type II spiral ganglion neurons show significant differences from their type I counterparts. A, Accommodation is represented as the maximum number of action potentials that a neuron is capable of firing during suprathreshold step depolarizations 240 msec in duration. For all panels, the light gray hatched bars labeled “Base” and dark gray hatched bars labeled “Apex” represent the type I neurons, whereas the circles above each bar represent the type II neurons from the base and apex. The horizontal lines above the two bars indicate statistically significant differences between the basal and apical type I neurons, vertical lines on the left represent statistically significant differences between the base type I and type II neurons, and vertical lines on the right represent statistically significant differences between the apical type I and type II neurons. No significant differences between apical and basal type II neurons were found for any of the electrophysiological parameters measured. ^*p < 0.05; ^**p < 0.01. B, The action potential latency, at electrophysiological threshold (the lowest voltage level at which an action potential was observed), was measured as the time from the stimulus onset to the peak of the action potential. C, Action potential duration, at electrophysiological threshold, was measured at the point halfway between the peak and nadir of the waveform. D, The slow component of the onset tau was measured with a single exponential fitted to the voltage change from onset of the stimulus, excluding any initial fast component, to the peak voltage. Measurements were taken from subthreshold recordings made just below electrophysiological threshold. E, The time course of the fast AHP decay was measured by fitting a single exponential starting just after the nadir of the action potential. F, The voltage level representing electrophysiological threshold was measured from the peak voltage achieved in slightly subthreshold responses to depolarizing current injection. G, The magnitude of inward rectification was determined by measuring the difference between the peak and the plateau voltages from hyperpolarizing responses that peaked at -185 ± 3 mV. H, The time course of the inward rectification was measured with single exponential fits to the traces that peaked at -185 ± 3 mV.