Heart Muscle & Conduction system

There are 3 types of muscle in our body. Skeletal muscles which are present in our hands, legs and back and are responsible for our movement, smooth muscles which are present in our intestines, blood vessels and other parts of the body and finally the cardiac muscle or the myocardium which forms the heart. The heart muscle or the myocardium is very special and built in a way that allows it to do the job it was created for.

Unlike other types of muscle, heart muscle is relatively very strong and resistant to fatigue. In an adult, the heart beats about 75 times a minute or more and surprisingly, it never gets tired. The heart pumps about five liters of blood every single minute.

Heart muscle has another unique quality. The fibers that make up the heart muscle are connected by electrical conduction mechanisms called intercalated. These allow current to flow from one muscle-fiber cell to another so if one part of the heart is stimulated, the current will flow through all of the heart muscle causing the entire heart to contract.

Each heartbeat is the result of an electrical signal that passes through the heart. The electrical activity of the heart is called the heart’s rhythm, and can be measured by an electrocardiogram (ECG).

The heart has its own natural pacemaker, called the sinus node. When the sinus node fires, an electrical signal passes through the atria (top chambers) of the heart, causing them to squeeze. When the atria contract, they “top off” the ventricles with blood. The electrical signal travels to the atrioventricular (AV) node, where it is held for a split second. This allows time for the ventricles to fill completely with blood. The electrical signal then continues into the ventricles, through fibers called the bundle of His and from there throughout the ventricles causing them to contract.

This electrical impulse moves through the heart very fast, causing the heart to contract as a single unit. If something happens to the S-A node, such as disease or traumatic injury, the A-V node can take over as the heart’s pacemaker and so on with every single part of the electrical conducting system of the heart.