1. Electrical Conduction:
* Sinoatrial (SA) Node: The heart's natural pacemaker, located in the right atrium, initiates the electrical impulse.
* Internodal Pathways: The impulse travels through specialized pathways to the atrioventricular (AV) node.
* Atrioventricular (AV) Node: This node delays the impulse briefly to allow the atria to fully contract and empty before the ventricles receive the signal.
* Bundle of His: The impulse then travels down the Bundle of His, a pathway in the septum (wall) separating the ventricles.
* Purkinje Fibers: These fibers branch out from the Bundle of His and distribute the electrical signal throughout the ventricle walls.
2. Mechanical Contraction:
* Atrial Contraction: The electrical impulse triggers contraction of the atria, pushing blood into the ventricles.
* Ventricular Contraction: The impulse reaches the ventricles, causing them to contract forcefully, pumping blood out of the heart:
* Right ventricle: Pushes deoxygenated blood to the lungs.
* Left ventricle: Pushes oxygenated blood to the rest of the body.
3. Relaxation and Refill:
* Ventricular Relaxation: The ventricles relax, allowing them to fill with blood from the atria.
* Atrial Relaxation: The atria relax, preparing for the next cycle.
The Cycle Repeats: The electrical impulse from the SA node triggers the next heartbeat, and the process begins again.
Visualizing the Heartbeat:
* Electrocardiogram (ECG/EKG): This test records the electrical activity of the heart, providing a visual representation of the heartbeat. The characteristic "P wave" represents atrial contraction, the "QRS complex" indicates ventricular contraction, and the "T wave" reflects ventricular relaxation.
Important Note: This is a simplified explanation. The actual process involves complex interactions of electrical signals, muscle fibers, and pressure gradients.
