Action Potential Steps

Depolarization: Voltage-gated Na+ channels open (when threshold potential of -55mV is reached) and Na+ rushes INTO the axon (more Na+ outside of the cell), causing more Na+ channels to open - domino effect (propagation) DOWN THE AXON - MEMBRANE POTENTIAL BECOMES MORE POSITIVE.

Repolarization: K+ channels open (Na+ channels close) and K+ rushes OUT of the axon, triggering a domino effect down the axon. This causes MEMBRANE POTENTIAL TO BE MORE NEGATIVE - BECOMES HYPERPOLARIZED).

Resting potential restored (by sodium-potassium pumps: 3 Na+ OUT for every 2 K+ IN): This is known as the REFRACTORY PERIOD (another action potential CANNOT be fired until this period is complete - until the resting potential AND Na+/K+ ion concentration gradients are restored).