The electrical impulse generated by the heart originates in the:

The electrical impulse generated by the heart originates in the:

• A. Atrioventricular node.
• B. Sinoatrial node.
• C. Coronary sinus.
• D. Bundle of His.

Answer: (B)

The impulse starts in the heart’s natural pacemaker, the sinoatrial node, which sits in the wall of the right atrium. Its cells have the fastest automaticity, spontaneously firing action potentials and setting the pace for the heart. This impulse then spreads quickly across the atria to trigger atrial contraction, reaches the atrioventricular node where a brief delay allows the ventricles to fill, and continues down the His-Purkinje system to drive ventricular contraction. The coronary sinus, by contrast, is a venous channel draining blood from the heart into the right atrium and does not initiate electrical activity. If the SA node fails, other areas can pace the heart but at slower rates, which is why the SA node is the origin of the impulse.

The impulse starts in the heart’s natural pacemaker, the sinoatrial node, which sits in the wall of the right atrium. Its cells have the fastest automaticity, spontaneously firing action potentials and setting the pace for the heart. This impulse then spreads quickly across the atria to trigger atrial contraction, reaches the atrioventricular node where a brief delay allows the ventricles to fill, and continues down the His-Purkinje system to drive ventricular contraction. The coronary sinus, by contrast, is a venous channel draining blood from the heart into the right atrium and does not initiate electrical activity. If the SA node fails, other areas can pace the heart but at slower rates, which is why the SA node is the origin of the impulse.