Comparison of ionic and gating currents with the HH model. (a–d, top) Sodium gating currents (a and c) and sodium ionic currents (b and d) for a depolarizing pulse (a and b) and during repolarization (c and d). Adapted from Armstrong and Bezanilla (1974). Superimposed and scaled gating current (orange trace) and sodium current (blue trace) computed with the HH equations (bottom). The axon was held at V = −70 mV, and V was stepped to 0 at the up arrow and returned to −70 mV at the down arrow. Computed gating curents have been scaled so that the peak of computed ionic and gating currents coincide at pulse OFF.