The heart beat is controlled by a specialized group of cells in the heart called the sinoatrial (SA) node, often referred to as the heart's natural pacemaker. Here's a step-by-step explanation of how the heart beat is controlled:
1. Sinoatrial (SA) Node: The SA node is located in the right atrium of the heart. It generates electrical impulses that spread through the atria, causing them to contract and push blood into the ventricles.
2. Atrioventricular (AV) Node: The electrical signals from the SA node reach the atrioventricular (AV) node, which acts as a relay station. It briefly delays the electrical impulse to allow the ventricles to fill with blood before contracting.
3. Bundle of His and Purkinje Fibers: After passing through the AV node, the electrical signals travel down the Bundle of His and Purkinje fibers, which are specialized pathways that distribute the impulses rapidly to the ventricles.
4. Ventricular Contraction: The electrical impulses cause the ventricles to contract, pumping blood out of the heart to the lungs and the rest of the body.
5. Autonomic Nervous System: The autonomic nervous system, which consists of the sympathetic and parasympathetic divisions, modulates the heart rate. The sympathetic division increases heart rate during times of stress or excitement, while the parasympathetic division slows it down during rest and relaxation.
In summary, the heart beat is controlled by a precise sequence of electrical impulses originating from the SA node, traveling through the heart's specialized conduction system, and modulated by the autonomic nervous system to meet the body's needs for oxygen and nutrients.
