hjärtmuskeln

Hjärtmuskeln, known scientifically as the myocardium, is the specialized muscle tissue that forms the wall of the heart. Its primary function is to pump blood throughout the body through rhythmic contractions. Unlike skeletal muscle, which is under voluntary control, or smooth muscle, found in organs like the digestive tract, cardiac muscle is involuntary. This means its contractions are automatic and not consciously directed by the brain.

The cells that make up the hjärtmuskeln are called cardiomyocytes. These cells are unique in several ways. They are striated, meaning they have a striped appearance under a microscope, similar to skeletal muscle, due to the arrangement of contractile proteins actin and myosin. However, cardiomyocytes are interconnected by specialized junctions called intercalated discs. These discs contain gap junctions, which allow electrical impulses to pass rapidly from one cell to another, enabling the heart to contract as a coordinated unit.

The heart's electrical system, starting with the sinoatrial (SA) node, initiates these impulses. The SA node acts as the heart's natural pacemaker, generating electrical signals that spread through the atria and then the ventricles, causing them to contract in sequence. The hjärtmuskeln is highly resistant to fatigue, allowing it to perform its continuous pumping action from before birth until death. Its efficient energy metabolism, primarily relying on aerobic respiration, is crucial for this sustained activity. Damage to the hjärtmuskeln, such as from a heart attack, can impair its ability to pump blood effectively, leading to serious health consequences.