Action potential Exam 1

Resting State

Voltage gated Na⁺ and K⁺ channels are close; Resting membrane potential is maintained primarily by K⁺ leak channels

Depolarization

Membrane depolarizes toward threshold; Voltage gated Na⁺ channels begin to open

Rising Phase

Rapid activation of voltage-gated Na⁺ channels

Na⁺ influx drives membrane depolarization

Voltage-gated K⁺ channels begin activating

Overshoot

Membrane potential becomes positive

Na⁺ conductance remains high; Na⁺ channels begin to inactivate

Falling phase

Na⁺ channels become inactivated

K⁺ conductance increase; K⁺ efflux repolarizes the membrane

Undershoot

K⁺ channels remain open longer than necessary

Continued K⁺ efflux drives membrane potential below resting levels

Refractory period

Na⁺ channels recover from inactivation

Membrane returns to resting excitability