Final answer:
The action potential that causes the right and left atria to contract originates from the sinoatrial (SA) node, the heart's pacemaker, and, after a brief delay at the atrioventricular (AV) node, progresses through the heart's electrical conduction system to the ventricles.
Step-by-step explanation:
The right and left atria depolarize and contract following the arrival of the action potential from the sinoatrial (SA) node, which is the heart's natural pacemaker
The electrical charge spontaneously generated by the SA node causes the atria to contract. After this, the pulse of electricity reaches the atrioventricular (AV) node. This node introduces a brief delay before the impulse continues to the heart's ventricles through the atrioventricular bundle (bundle of His), right and left bundle branches, and finally the Purkinje fibers, leading to the contraction of the ventricles. This orchestrated delay allows the atria to fully empty their contents into the ventricles before ventricular contraction begins, which is essential for efficient heart function.