The axonal action potential is an all-or-none electrical impulse modeled by the Hodgkin-Huxley equations. When an external stimulus depolarizes the axon membrane above the threshold potential (~-55 mV), voltage-gated Na⁺ channels open rapidly, driving rapid depolarization toward E_Na (+40 mV). Subsequent delayed rectifier K⁺ channel activation and Na⁺ channel inactivation repolarize the membrane back to resting potential (-70 mV).