Q.Trace the sequence of events that occur at the axonal membrane when a stimulus of adequate strength triggers an action potential, from depolarization through to repolarization.

[!TLDR] A stimulus opens Na+ channels → Na+ rushes in → depolarization (inside becomes positive); Na+ channels then close and K+ channels open → K+ rushes out → repolarization, with a brief hyperpolarization before rest is restored. [!ANSWER] Stimulus → Na+ influx → depolarization (peak ~+30 to +40 mV) → Na+ channels inactivate, K+ channels open → K+ efflux → repolarization → brief hyperpolarization → resting potential restored.

When a stimulus of adequate strength reaches a point on the axon, voltage-gated Na+ channels open, and because Na+ is far more concentrated outside the cell, it rushes in; the inside of the membrane rapidly becomes positive relative to the outside, a swing called depolarization, typically overshooting to about +30 to +40 mV at the peak. The Na+ channels then quickly inactivate, stopping further Na+ entry, while the slower voltage-gated K+ channels now open fully, letting K+ rush out down its concentration gradient — this restores the inside-negative state and is called repolarization. Because the K+ channels stay open a little longer than needed, the membrane briefly dips below the normal resting value (hyperpolarization) before the Na+-K+ pump restores the original ionic balance and the membrane returns to its resting potential, ready to fire again after a brief refractory period. [!ANSWER] Depolarization (Na+ in) → repolarization (K+ out) → brief hyperpolarization → return to resting potential, restored by the Na+-K+ pump.

Track which channel is open at each stage and which ion is therefore moving, and in which direction, to derive the potential change at each step.

Do not conflate depolarization and repolarization — depolarization is the RISE (Na+ entry), repolarization is the FALL back down (K+ exit); many students reverse these.