Final answer:
The SA node initiates the electrical signal, which travels through the conduction system of the heart, including the AV node, bundle of His, and Purkinje fibers, causing atrial and ventricular contractions.
Step-by-step explanation:
The SA node, AV node, bundle of His, and Purkinje fibers are all part of the cardiac conduction system.
The SA node, located in the right atrium, initiates the electrical signal that coordinates the contraction of the heart. The signal then travels through the atria, causing them to contract.
Next, the signal reaches the AV node, which acts as a delay to allow the atria to fully contract before the ventricles begin to contract. From the AV node, the signal travels down the bundle of His, then into the left and right bundle branches. These branches distribute the signal to the Purkinje fibers, which spread the signal through the ventricles, causing them to contract.