Electrical System of the Heart - Topic Overview
SA node and atria
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.
AV node and ventricles
After the electrical signal has caused your atria to contract and pump blood into your ventricles, the electrical signal arrives at a group of cells at the bottom of the right atrium called the atrioventricular node, or AV node. The AV node briefly slows down the electrical signal, giving the ventricles time to receive the blood from the atria. The electrical signal then moves on to trigger your ventricles.
When the electrical signal leaves the AV node, it triggers the following process:
- The signal travels down a bundle of conduction cells called the bundle of His, which divides the signal into two branches: one branch goes to the left ventricle, another to the right ventricle.
- These two main branches divide further into a system of conducting fibers that spreads the signal through your left and right ventricles, causing the ventricles to contract.
- When the ventricles contract, your right ventricle pumps blood to your lungs and the left ventricle pumps blood to the rest of your body.
After your atria and ventricles contract, each part of the system electrically resets itself.
How does the heart's electrical system regulate your heart rate?
The cells of the SA node at the top of the heart are known as the pacemaker of the heart because the rate at which these cells send out electrical signals determines the rate at which the entire heart beats (heart rate).
The normal heart rate at rest ranges between 60 and 100 beats per minute. Your heart rate can adjust higher or lower to meet your body's needs.
What makes your heart rate speed up or slow down?
Your brain and other parts of your body send signals to stimulate your heart to beat either at a faster or a slower rate. Although the way all of the chemical signals interact to affect your heart rate is complex, the net result is that these signals tell the SA node to fire charges at either a faster or slower pace, resulting in a faster or a slower heart rate.