Which statement accurately describes the SA node and AV node in the cardiac conduction system?

• A. SA node acts as the natural pacemaker initiating impulses; AV node delays the signal to coordinate atrial and ventricular contraction.
• B. SA node delays the signal; AV node initiates impulses.
• C. SA node conducts impulses through the ventricles.
• D. SA node stores blood; AV node pumps.

Answer: (A)

The key idea is how the heart’s rhythm is generated and synchronized. The SA node serves as the natural pacemaker, generating impulses on its own to set the heart rate. The impulse then reaches the AV node, which acts as a gatekeeper by delaying the signal briefly. That delay gives the atria time to contract and push blood into the ventricles before the ventricles themselves contract. After the AV node, the signal travels through the His-Purkinje system to drive ventricular contraction. This arrangement—SA node initiating impulses and the AV node delaying them to coordinate atrial and ventricular activity—is why that statement is correct. The AV node does not initiate impulses, and the SA node does not conduct through the ventricles or store blood.