Figure 8. Single cell APs are stimulated with small, brief current pulses.

A, representative AP elicited by a 1 ms duration, 40 pA current injection (continuous line) superimposed on the V_m response to a subthreshold stimulus (dashed line). Constant holding current maintained MDP ∼−65 mV (29 pA in this example). B, a supra-threshold stimulus (50 pA) elicits an AP upstroke (continuous line) with a rapid V_max. Dashed line superimposed on AP is the AP derivative to illustrate dV/dt_max (V_max). Note the expanded time scale relative to A to illustrate rate of rise of AP. C, a subset of 9 cells in which Na⁺ current was recorded following single cell APs. V_max is plotted as a function of Na⁺ current. Linear regression (R) = 0.71.