Question: Describe the pothway of the electrical impulse during excitation of the heart muscle.

The pathway of an electrical impulse during the excitation of heart muscle is as follows:<br /><br />1. **Sinoatrial (SA) Node:** The impulse originates in the SA node, located in the upper wall of the right atrium. The SA node is known as the heart's natural pacemaker because it initiates the heartbeat. It generates electrical impulses spontaneously and rhythmically.<br /><br />2. **Interatrial Pathways:** The impulse spreads rapidly through the atrial muscle via specialized pathways (Bachmann's bundle being the most prominent), causing both atria to contract simultaneously. This pushes blood from the atria into the ventricles.<br /><br />3. **Atrioventricular (AV) Node:** The impulse then reaches the AV node, located in the lower part of the right atrium near the interatrial septum. The AV node delays the impulse briefly (about 0.1 seconds). This delay allows the atria to fully contract and empty their blood into the ventricles before the ventricles contract.<br /><br />4. **Bundle of His:** After the delay, the impulse travels down the Bundle of His, a specialized conducting pathway located in the interventricular septum.<br /><br />5. **Right and Left Bundle Branches:** The Bundle of His divides into right and left bundle branches, which carry the impulse down the right and left sides of the interventricular septum, respectively.<br /><br />6. **Purkinje Fibers:** Finally, the impulse spreads through the Purkinje fibers, a network of specialized conducting fibers that extend throughout the ventricular myocardium. This rapid distribution of the impulse causes both ventricles to contract simultaneously and forcefully, pushing blood out of the heart and into the pulmonary artery (from the right ventricle) and the aorta (from the left ventricle).<br /><br /><br />This coordinated electrical activity ensures that the heart beats efficiently, effectively pumping blood throughout the body.<br />