Sinoatrial Node as Atrial Pacemaker

Steps:

• Recall the heart's electrical system starts in the atria with the sinoatrial (SA) node as the primary pacemaker.
• Note that SA node damage disrupts initial atrial stimulation, leading to irregular heartbeats like atrial fibrillation.
• Evaluate options: SA node directly controls atrial depolarization.
• Confirm other structures handle conduction downstream or are non-electrical.

Why D is correct:

• The sinoatrial node generates the initial electrical impulse that stimulates atrial contraction, per cardiac conduction physiology.

Why the others are wrong:

• A: Atrioventricular node relays impulses from atria to ventricles, not initiating atrial stimulation.
• B: Septum is a structural wall dividing heart chambers, unrelated to electrical conduction.
• C: Purkinje tissue conducts impulses to ventricular myocardium, not atria.

Final answer: D