CVS Practice Test 2025 – The All-In-One Guide to Exam Success!

The sinoatrial (SA) node is primarily composed of specialized cells known as pacemaker cells and transitional cells. These pacemaker cells are crucial for initiating and regulating the heart's rhythm, effectively setting the pace for cardiac contractions. They possess unique properties that allow them to generate spontaneous action potentials, which subsequently propagate through the heart's conduction system to trigger contractions.

Transitional cells in the SA node serve to connect the pacemaker cells with regular cardiac muscle cells, ensuring efficient signal conduction. This unique cellular composition is essential for maintaining the heart's innate ability to beat rhythmically and respond appropriately to physiological changes.

In contrast, cardiac muscle cells are typically found in other areas of the heart, specifically responsible for contraction, but they do not have the pacemaking ability inherent to the cells of the SA node. Neurotransmitter cells are not involved in the structural composition of the heart and are primarily associated with the nervous system. Contractile cardiomyocytes are also not dominant in the SA node; they play a larger role in the heart muscle that contracts to pump blood rather than in the specialized conduction system that regulates heartbeat initiation.