Figure 8.

A: Schematic of voltage-gated Na⁺ current (I_Na; red), Ca²⁺ current (I_Ca; green), delayed rectifying K⁺ current (I_K; blue) and total membrane current (I_total, i.e. I_Na + I_Ca + I_K; black) elicited by a voltage-clamp depolarization (V) from -70 mV to -10 mV. The dashed line indicates the zero-current level. Downward and upward deflections represent inward (depolarizing) and outward (repolarizing) membrane currents, respectively. B: Time-dependent changes in the value of m (dotted red), m³ (continuous red) and h (grey) where m and h vary with time after the onset of depolarization (t) according to the expressions m(t) = m_{∞ *} (1-exp[-t/τ_m]) and h(t) = h₀ * exp(-t/τ_h). The parameter values for m and h have been normalized to their maximum. The green trace (below) shows the product m³h, which approximates the activation and inactivation of the whole-cell Na⁺ current. The curve has been inverted in order to facilitate comparison with the Na⁺ current. C: Time-dependent changes in values of n and n⁴ where n varies with time after onset of depolarization (t) according to the expression n(t) =n_∞*(1-exp[t/τ_n]). This approximates the time course of the whole-cell K⁺ current. Note that m³ and n⁴ result in sigmoidal activation kinetics. Modified from (282).