Final answer:
The SA node, located in the right atrium, is responsible for establishing the normal cardiac rhythm and is commonly referred to as the heart's pacemaker, initiating the contraction and coordination of the heart muscle.
Step-by-step explanation:
The SA node, or sinoatrial node, is a crucial component of the cardiac conduction system and is also known as the pacemaker of the heart. This group of specialized myocardial conducting cells is located in the superior and posterior walls of the right atrium, near the entry of the superior vena cava. The SA node is responsible for initiating the sinus rhythm, which is the normal electrical pattern that causes the heart muscle to contract. It does this by creating electrical signals through the movement of electrolytes such as sodium, potassium, and calcium ions. After the SA node fires, the electrical impulse travels through the right and left atria, causing them to contract simultaneously. Then, the signal moves to the atrioventricular (AV) node and onto the ventricles, coordinating the heart's pumping action.