In the normal electrical conduction system of the heart, where does the electrical impulse travel immediately after it leaves the AV node?

Choice A rationale The atrial myocardium is stimulated by the electrical impulse originating in the sinoatrial (SA) node. The impulse spreads through the atria to cause contraction before reaching the atrioventricular (AV) node. Once the impulse reaches the AV node, it undergoes a brief delay to allow the ventricles to fill with blood. Therefore, the impulse has already passed through and finished stimulating the atrial myocardium by the time it exits the AV node to move downward. Choice B rationale In the normal sequence of cardiac conduction, the electrical impulse travels from the atrioventricular (AV) node directly into the Bundle of His. The Bundle of His serves as the critical bridge that allows the electrical signal to pass from the atria into the ventricles. This pathway is the only physiological electrical connection between the upper and lower chambers. From here, the impulse will bifurcate into the right and left bundle branches to reach the lower ventricles. Choice C rationale The Purkinje fibers represent the final stage of the cardiac conduction system. They are located deep within the ventricular walls and are responsible for the rapid depolarization and subsequent contraction of the ventricular myocytes. The electrical impulse does not reach these fibers until after it has traveled through the AV node, the Bundle of His, and the left and right bundle branches. Reaching the Purkinje fibers is the terminal step before the entire ventricle contracts. Choice D rationale The sinoatrial (SA) node is the primary pacemaker of the heart where the electrical impulse is originally generated. The signal moves from the SA node to the AV node, not the other way around. If the electrical impulse were to move from the AV node back to the SA node, it would be considered retrograde conduction, which is an abnormal finding often seen in certain arrhythmias but not in the normal electrical system.