Which nodes control the heart's electrical signals?

• A. SA node & AV node
• B. AV node & Bundle of His
• C. SA node only
• D. Purkinje fibers

Answer: (A)

The heart’s rhythm is governed by the conduction system, with two key nodes taking the lead: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node acts as the primary pacemaker, generating impulses at a natural rate and setting the pace of the heart. The impulse then travels to the AV node, which serves as a crucial relay and introduces a brief delay. That delay allows the atria to finish contracting and push blood into the ventricles before the ventricles themselves are stimulated to contract.

If the SA node slows or fails, the AV node can take over as a backup pacemaker, but typically at a slower rate, which is why the coordinated timing between atrial and ventricular contractions is maintained under normal conditions by both nodes working together. The Bundle of His and Purkinje fibers are important conduits that carry the impulse into the ventricles, but they do not set the heart’s pace or primarily regulate initiation; they distribute the signal.

So, the two nodes that control the heart’s electrical signals are the SA node and the AV node.