Which statement best describes the SA node?

• A. It is the natural pacemaker of the heart
• B. It coordinates the timing of the heart's contractions
• C. It delays impulses in the conduction system
• D. It conducts impulses to the ventricles

Answer: (D)

The SA node acts as the heart’s natural pacemaker, generating regular electrical impulses that set the heart’s pace. This impulse starts here and then spreads through the atria to trigger atrial contraction, before reaching the AV node where a brief delay allows the ventricles to fill. From there, the signal travels through the His-Purkinje system to activate the ventricles. For this reason, the SA node’s defining role is initiating and setting the rate of heartbeats, not directly conducting impulses to the ventricles. The other statements either describe a role of different parts (such as delaying impulses at the AV node) or imply direct ventricular conduction from the SA node, which isn’t how the conduction pathway works.