Cardiac conduction system sequence

Steps:

• Impulse originates in sinoatrial node (4), the heart's pacemaker.
• It spreads through atrial muscle walls (2), causing atrial contraction.
• Impulse reaches atrioventricular node (1), which delays it briefly.
• From AV node, impulse travels via bundle of His to Purkinje fibers (3) in ventricles.

Why C is correct:

• C follows the defined cardiac conduction pathway: SA node initiates, atria depolarize, AV node relays, Purkinje conducts to ventricles.

Why the others are wrong:

• A: Starts at AV node, but SA node initiates impulse.
• B: Begins with AV node before SA node, reversing pacemaker origin.
• D: Places Purkinje before atria, but atria contract first.

Final answer: C