During a normal human's lifetime, the heart beats an estimated three billion times. Each beat is coordinated by a sophisticated network of neural tissue known as the cardiac conduction system or CCS. The CCS generates lightning-fast electrical impulses which are rapidly conducted through the heart muscle. This impulse causes the heart chambers to contract in a rhythmic sequence, pumping blood throughout your body.
The elements comprising the CCS are the sinoatrial node (also referred to as the "SA node" or "pacemaker"), the atrioventricular node ("AV node") and certain fibers of the autonomic nervous system referred to as the Bundle of His.
The sinoatrial node is a small lump of neural tissue located in the right atrium of the heart. This tiny cluster of cells is responsible for initiating the electrical impulse that causes the heart to beat. This impulse travels rapidly throughout the cells of the atria causing them to contract then continues on to the AV node.
Located near the center of the heart, the AV node serves as a kind of "gatekeeper" delaying the electrical impulse before relaying it on to stimulate the ventricles. This slight delay ensures that the right and left atria have had sufficient time to contract before the ventricles do.
From here, the impulse travels on to the right and left ventricles by way of the bundle of His. These specialized autonomic nerve fibers are located inside the muscular walls of the heart. The impulse is passed through the muscle cells of the ventricles causing them to contract and forcefully eject the blood contained within.
Once complete, the cycle begins again to keep your heart beating... and your blood flowing.
Source: Nucleus Medical Art, Inc.
Last Reviewed: December, 2003