Visualize how neurons fire and signals propagate along an axon.
Neurons have a resting potential of −70 mV. When a stimulus reaches the threshold (−55 mV), voltage-gated Na⁺ channels open → rapid depolarization to +30 mV. K⁺ channels then open → repolarization, followed by a brief hyperpolarization. This is an all-or-nothing response. The signal propagates down the axon as a wave of depolarization.