Which sequence does the electrical stimulus of the cardiac cycle follow?

A. SA node → AV node → bundle branches → Purkinje fibers: The sinoatrial (SA) node, located in the right atrium, is the heart's natural pacemaker, initiating electrical impulses. These impulses travel to the atrioventricular (AV) node, where conduction slows to allow ventricular filling. The signal then moves through the bundle of His, dividing into the right and left bundle branches, and finally reaches the Purkinje fibers, which stimulate ventricular contraction. This is the correct sequence. B. AV node → SA node → Purkinje fibers → bundle branches: The AV node does not initiate the electrical impulse under normal conditions; it receives the impulse from the SA node. The Purkinje fibers are the final part of the conduction pathway, not an intermediate step before the bundle branches. C. Bundle branches → AV node → SA node → Purkinje fibers: Electrical conduction does not begin at the bundle branches. The SA node initiates the impulse, and the AV node delays transmission before passing the impulse to the ventricles via the bundle branches and Purkinje fibers. D. AV node → SA node → bundle branches → Purkinje fibers: The SA node, not the AV node, initiates the cardiac cycle. The AV node functions as a relay station that briefly delays the impulse before it proceeds to the bundle branches and Purkinje fibers.