Muscle Fibers Muscle fibers are the basic building blocks of muscle tissue. In skeletal muscle, these fibers are bundled together into fascicles, which are then grouped to form the entire muscle. Each muscle fiber contains myofibrils, which are composed of repeating units called sarcomeres. Sarcomeres are the functional units of muscle contraction and contain the actin and myosin filaments.
Sarcomere The sarcomere is the fundamental unit of muscle contraction in both skeletal and cardiac muscle. It is defined by the area between two Z-discs. Within the sarcomere, the actin (thin) and myosin (thick) filaments slide past each other to produce contraction. The arrangement of these filaments gives skeletal and cardiac muscles their striated appearance.
