AV Node Delays Impulse for Coordinated Heartbeat

Steps:

• Recall the heart's electrical conduction system starts at the sinoatrial (SA) node in the right atrium.
• Trace the impulse path: SA node fires, spreads through atria, reaches atrioventricular (AV) node at the atrial-ventricular junction.
• Identify AV node's function: it briefly delays the impulse to allow atria to fully contract before ventricles do.
• Eliminate options by matching to conduction roles: delay fits B, while others misattribute initiation, contraction direction, or barriers.

Why B is correct:

• The AV node delays the electrical impulse by about 0.1 seconds, ensuring atrial contraction completes before ventricular depolarization begins, per cardiac physiology principles.

Why the others are wrong:

• A: Ventricular contraction direction is apex upward due to Purkinje fibers, not AV node.
• C: AV node relays but does not initiate ventricular activity; that's the bundle of His and Purkinje system.
• D: No non-conducting barrier exists; AV node conducts with delay, unlike fibrous skeleton separating atria and ventricles elsewhere.

Final answer: B