Atrial action potential

Atrial action potential refers to the electrical changes that occur in atrial myocytes, which are the muscle cells of the atria in the heart. These changes are crucial for the initiation and propagation of the cardiac cycle, which is the sequence of events that occur when the heart beats.

Overview

The atrial action potential is initiated by the sinoatrial node, the heart's natural pacemaker. This triggers a wave of depolarization that spreads through the atria, causing them to contract and pump blood into the ventricles.

Phases of the Atrial Action Potential

The atrial action potential consists of five phases, numbered 0 through 4.

Phase 0

Phase 0 is the rapid depolarization phase. It is initiated when the membrane potential reaches a certain threshold, causing voltage-gated sodium channels to open. This allows sodium ions to rush into the cell, causing the membrane potential to become positive.

Phase 1

Phase 1 is the initial repolarization phase. After the sodium channels close, voltage-gated potassium channels open. This allows potassium ions to leave the cell, causing the membrane potential to start to become negative again.

Phase 2

Phase 2 is the plateau phase. During this phase, calcium ions enter the cell through calcium channels, balancing the outflow of potassium ions. This causes the membrane potential to remain relatively stable.

Phase 3

Phase 3 is the rapid repolarization phase. The calcium channels close and more potassium channels open, causing the membrane potential to become more negative.

Phase 4

Phase 4 is the resting phase. During this phase, the membrane potential is maintained at a stable negative value until the next action potential is initiated.

Clinical Significance

Abnormalities in the atrial action potential can lead to arrhythmias, which are irregular heart rhythms. For example, if the atrial action potential is too long, it can lead to atrial fibrillation, a condition in which the atria beat irregularly and out of sync with the ventricles.

See Also

• Cardiac action potential
• Ventricular action potential
• Pacemaker potential