Cardiac action potential

A transient change in a heart cell’s membrane voltage, produced by ion currents across its membrane. Its shape and timing trigger contraction in working muscle cells or regulate rhythm in pacemaker cells.

Cardiac action potential phases: The successive voltage changes that make up a cardiac cell’s action potential. The phases show how ion currents shape the cardiac waveform over time.
Membrane potential: The electrical voltage difference between the inside and outside of a cell membrane. A cardiac action potential is a rapid, organized change in this voltage.
Electrocardiogram: A recording of voltage differences at the body surface generated by the heart’s electrical activity. Its waves reflect the summed activation and recovery of cardiac cells.
Pacemaker action potential: An action potential in a cardiac pacemaker cell, marked by spontaneous diastolic depolarization and no stable resting voltage. It contrasts with the stable resting potential and rapid upstroke of working myocardial cells.
Refractory period: An interval after excitation when a cell cannot, or is less able to, generate another action potential. The long cardiac refractory period prevents sustained contraction and limits rapid re-excitation.
Voltage-gated sodium channel: A membrane protein that opens in response to voltage changes and allows sodium ions to cross. Fast sodium entry initiates the steep upstroke in working atrial and ventricular cells.
Electrochemical gradient: The combined effect of a concentration difference and an electrical force on an ion. Ion gradients provide the driving forces behind cardiac membrane currents.
Cardiac arrhythmia: A disturbance in the rate, regularity, or origin of the heartbeat. Abnormal impulse formation or propagation can disrupt the normal sequence of action potentials.
Ventricular action potential: The characteristic action potential of ventricular muscle cells, with a rapid upstroke and prolonged plateau. It is the best-known working-cell waveform and differs from nodal-cell activity.
Excitation–contraction coupling: The processes that connect electrical excitation of a muscle cell to its mechanical contraction. The cardiac action potential supplies the calcium signal that links excitation to force.

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