szarkomériákat

A szarkoméria, often referred to as a sarcomere in English, is the fundamental contractile unit of skeletal and cardiac muscle tissue. It is the smallest repeating structural and functional unit of a myofibril, the long protein filaments that make up muscle fibers. Each sarcomere is defined by its boundaries, called Z-lines or Z-discs, which are thin, dense protein structures.

Within a sarcomere, several types of protein filaments interact to produce muscle contraction. The thick filaments are primarily composed of the protein myosin, while the thin filaments are mainly composed of the protein actin. These filaments are arranged in a highly organized manner. The region between the Z-lines is characterized by an overlap of thick and thin filaments.

The visible banding pattern in striated muscle, consisting of alternating light and dark bands, is a result of the precise arrangement of these filaments within the sarcomeres. The dark bands, known as A-bands, contain the entire length of the thick myosin filaments, and also overlap with thin actin filaments. Within the A-band, there is a lighter region called the H-zone, which contains only myosin filaments. The light bands, known as I-bands, contain only thin actin filaments and span from the end of one myosin filament to the beginning of the next. The M-line, located in the center of the H-zone, is a protein structure that anchors the myosin filaments.

During muscle contraction, the Z-lines are pulled closer together, shortening the sarcomere. This shortening is caused by the sliding of the actin filaments over the myosin filaments, a process driven by the interaction of myosin heads with actin binding sites, fueled by ATP. This sliding filament theory explains the mechanism of muscle contraction at the sarcomere level.