Which statement correctly describes the sinus node?

• A. It is located in the left ventricle and is the slowest pacemaker.
• B. It has no role in setting heart rate.
• C. It functions as the normal pacemaker of the heart because it has the highest rate of automaticity.
• D. It is responsible for ventricular depolarization.

Answer: (C)

The key idea is that the sinus (SA) node is the heart’s natural pacemaker because it has the highest rate of automaticity, so it normally sets the heart rate.

The SA node, located in the right atrium near the superior vena cava, generates impulses that dictate the rhythm of the heart. Its intrinsic firing rate is faster than other pacemaker areas, typically within about 60–100 beats per minute in adults, which establishes the normal sinus rhythm. The impulse then travels through the atria to the AV node and onward via the His–Purkinje system to depolarize the ventricles. It does not directly cause ventricular depolarization, and it is not located in the left ventricle.

If the SA node slows or fails, other pacemakers (like the AV node or Purkinje system) can take over, but they fire at slower rates. This is why the statement about the SA node being the normal pacemaker because of its highest rate of automaticity is the correct one.