THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -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-2: -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-3: -The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The atria are then activated. The electrical stimulus travels down through the conduction pathways and causes the heart’s ventricles to contract and pump out blood.

Detailed explanation-4: -The SA node is considered the pacemaker of the heart. Its electrical signals normally cause the atria of an adult’s heart to contract at a rate of about 60 to 100 times a minute. Disturbance anywhere along this electrical pathway can cause irregular heartbeats (arrhythmia).