CVS Practice Test 2026 - Free CVS Practice Questions and Study Guide

Automaticity in cardiac muscle fibers refers to the ability of certain heart cells, particularly within the sinoatrial (SA) node, to depolarize spontaneously without external stimulation. This intrinsic capacity to generate action potentials is crucial for initiating the heart's rhythmic contractions and controlling the heartbeat.

Spontaneous depolarization occurs due to the unique ion channel activity in these cardiac cells, allowing them to gradually depolarize until they reach a threshold, triggering an action potential. This mechanism ensures that the heart can set its own rhythm, making it an essential characteristic of cardiac muscle.

The other options do not accurately reflect the nature of automaticity. Regular repolarization refers to the process of returning to a resting state after depolarization and is a different aspect of the cardiac cycle. Voluntary contraction suggests control over the muscle fibers, which contradicts the involuntary nature of cardiac muscle. Dependency on neural input implies that the heart relies on signals from the nervous system, which is not true for the cells exhibiting automaticity, as they can function independently.