FIGURE 3. Effect of the shape of the sodium channel activation curve and effective peak conductance on action potential initiation in a Hodgkin–Huxley-type model.

Activation curves used in the model (a, c, e) and initial phases of resulting action potentials (b, d, f) are shown using matched colours. Blue lines show standard activation curves¹⁴. a, b, Increasing the steepness of the activation curve (a) leads to a more rapid action potential upstroke (b). Dashed lines indicate tangents at 10 mV ms^-1. c–f, Initiation of action potentials with shallow (c, d) and steep (e, f) activation curves and different sodium peak conductances in a model driven by fluctuating synaptic inputs (several action potentials superimposed). Changing peak conductance shifts the action potential onset potential but does not affect its onset rapidness. Steeper activation curves lead to smaller action potential onset spans (d, 6 mV; f, 2.5 mV).