action potentials

Resting potential Pacemaker Cells (SA Node)

None (unstable, slowly rises)

Resting potential Cardiac Muscle Cells (Myocardium)

Stable at –90 mV

Depolarization trigger

Ca²⁺ influx via voltage-gated channels

Depolarization trigger

Na⁺ influx

Repolarization Pacemaker Cells (SA Node)

K⁺ efflux

Repolarization Cardiac Muscle Cells (Myocardium)

K⁺ efflux

Special phase Pacemaker Cells (SA Node)

Pacemaker potential (leaky Na⁺)

Special phase Cardiac Muscle Cells (Myocardium)

Plateau phase (slow Ca²⁺ entry)

Refractory period Pacemaker Cells (SA Node)

Short

Refractory period Cardiac Muscle Cells (Myocardium)

Long → prevents cramping