The Hodgkin-Huxley model describes how action potentials in neurons are initiated and propagated through a set of nonlinear differential equations:
\[ \begin{aligned} C_m \frac{dV}{dt} &= -\bar{g}_\text{Na} m^3 h (V - E_\text{Na}) - \bar{g}_\text{K} n^4 (V - E_\text{K}) - \bar{g}_\text{L} (V - E_\text{L}) + I_\text{ext},\\[1mm] \frac{dm}{dt} &= \alpha_m(V)(1-m) - \beta_m(V)m,\\[1mm] \frac{dh}{dt} &= \alpha_h(V)(1-h) - \beta_h(V)h,\\[1mm] \frac{dn}{dt} &= \alpha_n(V)(1-n) - \beta_n(V)n. \end{aligned} \]
where \(V\) is the membrane potential, \(m\), \(h\), and \(n\) are gating variables, and \(I_\text{ext}\) is the external current stimulus.