Hodgkin-Huxley neuron model — Na⁺/K⁺ conductances and the action potential spike
Hodgkin & Huxley (1952, Nobel 1963): C_m dV/dt = I_ext − g_Na·m³h·(V−E_Na) − g_K·n⁴·(V−E_K) − g_L·(V−E_L). Gating variables m,h,n follow dx/dt = α_x(V)(1-x) − β_x(V)x. The depolarization opens Na⁺ channels (inward current), which is terminated by Na⁺ inactivation (h gate) and K⁺ activation (n gate), giving the characteristic spike shape.