Human Cardiac and Respiratory Systems: Electrical Activity of the heart.

The heart has a specialised natural pacemaker known as the sino-atrial (SA) node. The sino-atrial node is responsible for making the heart beat and regulating the cardiac cycle. The heart is the only organ that acts independently of the brain, the SA node generates its own nerve impulses.

The SA node is located in the upper portion of the right atrium and when it sends an impulse it sets off a chain of events.

When it first fires, the electrical impulse travels across both of the atria making them contract, this forces blood within the atria to be pushed into the ventricles.

The impulse then moves to to the atrio-ventricular (AV) node, this is located just above the ventricles. The impulse is delayed for a brief period at the AV node. This delay allows the atria to empty the blood into the ventricles.

After the delay the impulse then travels throughout he ventricles via special pathways called purkinje fibres. This then stimulates the ventricles to contract forcing the blood out and into the pulmonary artery and the aorta.

This cycle happens around 72 times per minute.