A specialized mass of conducting cells located at the atrioventricular junction in the heart.

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

Answer: (D)

The atrioventricular node is a key relay point in the heart’s electrical system, located at the junction between the atria and ventricles. It receives the impulse from the sinoatrial node and introduces a brief delay so the atria can finish contracting and filling the ventricles before the signal proceeds. This pause is essential for coordinated heartbeat. After the delay, the impulse moves onward through the bundle of His and then the Purkinje fibers to activate the ventricles. The AV node also has a slower inherent firing rate, which allows it to act as a backup pacemaker if the primary pacemaker fails. The other structures have different locations and roles: the sinoatrial node is in the right atrium and is the primary pacemaker, the bundle of His conducts impulses through the interventricular septum, and the Purkinje fibers distribute the impulse throughout the ventricles.