Final answer:
An electrical impulse travels from the SA node to the atria, causing them to contract. The impulse then travels through specialized internodal pathways to the AV node and further into the ventricles, resulting in their contraction.
Step-by-step explanation:
An electrical impulse travels from the sinoatrial (SA) node to the walls of the atria, causing them to contract. This impulse spreads through specialized internodal pathways, including the anterior, middle, and posterior bands, which lead from the SA node to the atrioventricular (AV) node. From there, the impulse travels through the AV bundle, bundle branches, and Purkinje fibers, causing the ventricles to contract and pump blood throughout the body.