Which structure typically serves as the natural pacemaker of the heart?

Which structure typically serves as the natural pacemaker of the heart?

• A. Atrioventricular node
• B. Sinoatrial node
• C. Bundle of His
• D. Purkinje fibers

Answer: (B)

The heart’s natural pacemaker is the sinoatrial node because its cells have the highest intrinsic rate of automatic depolarization and initiate the electrical impulses that set the heart’s rhythm. Located in the right atrium near the opening of the superior vena cava, it fires spontaneously to generate a regular heartbeat, typically around 60–100 beats per minute in a healthy adult. This pacemaker activity drives the timing of atrial contractions and sets the pace for the entire conduction system. If the SA node fails, the atrioventricular node can take over as a secondary pacemaker, but it fires more slowly, around 40–60 bpm, which slows the heart rate. TheBundle of His and Purkinje fibers mainly serve as pathways to conduct impulses to the ventricles and coordinate contraction rather than set the pace, so they aren’t natural pacemakers.

The heart’s natural pacemaker is the sinoatrial node because its cells have the highest intrinsic rate of automatic depolarization and initiate the electrical impulses that set the heart’s rhythm. Located in the right atrium near the opening of the superior vena cava, it fires spontaneously to generate a regular heartbeat, typically around 60–100 beats per minute in a healthy adult. This pacemaker activity drives the timing of atrial contractions and sets the pace for the entire conduction system. If the SA node fails, the atrioventricular node can take over as a secondary pacemaker, but it fires more slowly, around 40–60 bpm, which slows the heart rate. TheBundle of His and Purkinje fibers mainly serve as pathways to conduct impulses to the ventricles and coordinate contraction rather than set the pace, so they aren’t natural pacemakers.