The principles of electrical current flow in neurons are well understood, from studying the ‘equivalent circuits’ constructed from resistors and capacitors which represent the corresponding properties of the membrane and cytoplasm, and the differential equations describing the dynamics of the opening probabilities of NaV and KV channels as voltage changes. These can give quantitatively accurate predictions of the overall behaviour of the membrane potential, including action potential firing, both single and repetitive, during stimulation – famously in the Hodgkin–Huxley model.