How is a heartbeat generated?

The rhythmic contraction and relaxation of the heart, known as a heartbeat, is orchestrated by a specialized electrical conduction system within the heart. This system ensures that the heart chambers contract in a coordinated sequence, allowing for the efficient pumping of blood throughout the body.

1. Sinoatrial (SA) Node:

- The heartbeat originates in the sinoatrial node, also known as the natural pacemaker of the heart.

- Located in the right atrium, the SA node generates electrical impulses that initiate each heartbeat.

2. Atrioventricular (AV) Node and AV Bundle:

- The electrical impulse generated by the SA node travels to the atrioventricular node, located at the junction of the atria and ventricles.

- The AV node delays the impulse slightly, allowing the atria to fill with blood.

- The impulse then passes through specialized AV bundle branches, which rapidly conduct the impulse to the ventricles.

3. Bundle of His and Purkinje Fibers:

- The bundle of His divides into the left and right bundle branches, which carry the electrical impulse to the left and right ventricles.

- The Purkinje fibers are specialized conducting fibers within the ventricles. They distribute the electrical impulse throughout the ventricular walls, causing them to contract almost simultaneously.

4. Ventricular Contraction:

- As the electrical impulse spreads through the ventricles via the Purkinje fibers, it triggers the contraction of the ventricular muscles.

- This contraction forces blood out of the ventricles and into the pulmonary artery (from the right ventricle) and the aorta (from the left ventricle).

5. Atrial Repolarization and Ventricular Depolarization:

- After the ventricles contract, the electrical impulse causes the ventricular muscles to repolarize, or relax.

- During this repolarization phase, the atria depolarize and contract due to the spread of electrical impulses from the SA node. This atrial contraction helps fill the ventricles with blood in preparation for the next heartbeat.

The sinoatrial node sets the basic pace of the heartbeat, but its rate can be influenced by the autonomic nervous system, hormones, and other factors to adjust to the body's varying needs for blood circulation.