AP BIOLOGY

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 heart’s rhythm is controlled by a natural pacemaker (the sinus node) in the right upper chamber (atrium). The sinus node sends electrical signals that typically start each heartbeat. These electrical signals move across the atria, causing the heart muscles to squeeze (contract) and pump blood into the ventricles.

Detailed explanation-3: -Electrical pulses in the heart are controlled by special groups of cells called nodes. The SA (sinoatrial) node generates an electrical signal that causes the upper heart chambers (atria) to contract.

Detailed explanation-4: -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-5: -The sinoatrial node (SAN) is the dominant pacemaker of the heart, located at the junction of the superior vena cava and right atria, that regulates heart beat frequency [1]. Abnormalities in SAN formation and function cause sinus arrhythmia and sudden death.