When the SA node sends an electrical impulse, it triggers the following process: The electrical signal travels from your SA node through muscle cells in your right and left atria. The signal triggers the muscle cells that make your atria contract. The atria contract, pumping blood into your left and right ventricles.

What is the purpose of atrial contraction?

Atrial depolarization initiates contraction of the atrial musculature. As the atria contract, the pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular (AV) valves, leading to a rapid flow of blood into the ventricles.

Why do the atria contract before the ventricles?

The right and left atria are stimulated first and contract to push blood from the atria into the ventricles. The ventricles then contract to push blood out into the blood vessels of the body. ... This allows the atria to contract a fraction of a second before the ventricles.