Function of the Cardiac Muscle

Of the three main types of muscle in the human body, cardiac muscle is perhaps the least understood. This muscle, unlike the smooth or striated muscles found in the arms and legs, never seems to get tired. This is because the cardiac muscle is designed to keep going, every minute of every day, nonstop for decades. How? Keep reading.

• The cardiac muscle helps keep the body strong.

Cardiac Muscle Fibers

• Unlike smooth or striated muscle, cardiac muscle is not linear, but rather forms a branching, crisscross network of muscle fibers pulling in all directions. This is because cardiac muscle squeezes what is essentially a bulb. If the pressure is applied like a belt on a water balloon, some of the water will remain in the balloon. If the balloon is squeezed in all directions, all of the water is forced out. In this manner, cardiac muscle fibers form a mesh to squeeze the heart's chambers, forcing the blood either to the lungs or throughout the body.

T-Tubules in Cardiac Muscle

• T-tubules, or transverse tubules, are the pathways for electrical stimulation to get to and activate the muscle. In cardiac muscle, there are fewer T-tubules, but they are typically broader and larger, meaning more of a signal can get to and activate the muscle.

Cardiac Muscle Metabolism

• Cardiac muscle never seems to fatigue, despite the extreme stresses placed on it by constant use, often flexing and relaxing as much as twice every second or more. It keeps going thanks to an abundance of mitochondria. Mitochondria are the fuel plants for the cells. They take in the nutrients and generate adenosine triphosphate, or ATP, which is the source of chemical energy for the muscle.
  In addition, cardiac muscles can convert lactate into fuel, meaning the heart always has fuel, even when the rest of the body is starving for food.

Cardiac Muscle Electrical System

• In order to make the cardiac muscle work effectively, it has to have a specialized electrical system to send signals to the right section of muscle at the right time. This means there has to be a delay between the atrium and ventricle muscles to ensure all the blood within each chamber is pumped out. To do this, the heart uses the sinoatrial node, or SA node, to direct electrical impulses to the right section of the heart at the right time. The SA node also keeps a slight bit of tension on the muscles at all times to maintain consistent blood pressure and a state of readiness for the next contraction.

Cardiac Cell Regeneration

• Until recently, it was believed that cardiac cells did not regenerate and that those lost to heart attack or other damage were gone forever. A study in Stockholm that was published in the April 3, 2009, issue of Science found evidence that cardiac cells divided after creation, meaning the heart muscles do regenerate. The rate of regeneration, however, still is not known.