ANATOMY

Detailed explanation-1: -The atrioventricular node delays the SA node’s electrical signal. It delays the signal by a consistent amount of time (a fraction of a second) each time. The delay ensures that your atria are empty of blood before the contraction stops. The atria are the heart’s upper chambers.

Detailed explanation-2: -The SA (sinoatrial) node generates an electrical signal that causes the upper heart chambers (atria) to contract. The signal then passes through the AV (atrioventricular) node to the lower heart chambers (ventricles), causing them to contract, or pump.

Detailed explanation-3: -The autonomic nervous system tightly controls input into the sinus node. The autonomic fibers regulate the firing of the sinus node to initiate the start of subsequent cardiac cycles and thus, influence the heart rate.

Detailed explanation-4: -The SA node starts the sequence by causing the atrial muscles to contract. That’s why doctors sometimes call it the anatomical pacemaker. Next, the signal travels to the AV node, through the bundle of HIS, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract.

Detailed explanation-5: -The sinoatrial node (SA node) is a specialized myocardial structure that initiates the electrical impulses to stimulate contraction, and is found in the atrial wall at the junction of superior caval vein and the right atrium (Mikawa and Hurtado, 2007).