myofibrillákat

Myofibrils are the fundamental contractile units of muscle cells, also known as muscle fibers. These long, cylindrical organelles are packed tightly within the sarcoplasm of a muscle cell and are responsible for muscle contraction. Each myofibril is composed of numerous repeating units called sarcomeres.

Sarcomeres are the functional units of myofibrils and are characterized by their organized arrangement of protein filaments. The primary proteins involved are actin, a thin filament, and myosin, a thick filament. These filaments overlap in a specific pattern, creating the striated appearance characteristic of skeletal and cardiac muscle. The interaction between actin and myosin filaments, driven by the hydrolysis of ATP, is the basis of muscle contraction.

Within the sarcomere, actin filaments are anchored to structures called Z-lines, which define the boundaries of each sarcomere. Myosin filaments are located in the center of the sarcomere, forming the A-band. The region where actin and myosin overlap, and the region containing only myosin (the H-zone), are crucial for the sliding filament mechanism of muscle contraction. The coordinated shortening of thousands of sarcomeres within a myofibril results in the overall contraction of the muscle fiber.