Does Your Heart Stop When You Sneeze? - Science ABC

Anatomy Of The Heartbeat

You might recall the following picture of the human heart from your high school biology classes:

As you can see in the image above, the heart is divided into four chambers: left atrium, right atrium, left ventricle and right ventricle. There’s a valve that connects each atrium to its corresponding ventricle. There are also two more valves, the pulmonic valve and the aortic valve, which complete the entire set. Together, all these valves act like gates, which allow about 2,000 gallons of blood to flow from one direction to another with each heartbeat every day.

Now, let’s talk about how the heart actually beats. A heartbeat is the result of a small electric current produced by the cardiac conduction system, which, in simple words, can be considered the electrical system that runs the heart.

A heartbeat is stimulated by an electric impulse that travels down a certain pathway through the heart. The impulse starts in the sinoatrial node or SA node (also known as the heart’s natural pacemaker), which is a small bunch of specialized cells found in the right atrium. This impulse spreads through the walls of the atria and makes them contract, which consequently pushes blood into the ventricles.

Before the electrical impulse reaches the ventricles, it passes through the atrioventricular node (or AV node). This is actually a cluster of cells between the atria and ventricles that acts like a gate and slows down the incoming electrical signal before it gains entry to the ventricles.

At this juncture, the network of Purkinje fibers steps into the scene. The impulse reaches the muscular walls of the ventricles through this pathway of fibers and causes the ventricles to contract. Consequently, blood flows out of the heart to various organs of the body.

This is where the entire process culminates, but all of that only makes up a single heartbeat.