Microscopic Structure of Skeletal Muscle :
A skeletal muscle has regular, ordered groups of fascicles, muscle fibers, myofibrils, and myofilaments. A muscle fiber divides into even smaller parts. Within each fiber are strands of myofibrils. These long cylindrical Structures appear striped due to strands of tiny myofilaments. Myofilaments have two types of protein : actin (thin myofilaments) and myosin (thick myofilaments). The actin and myosin myofilaments align evenly, producing dark and light bands on the myofibril, causing the striated appearance of skeletal muscle. The region between two Z lines is a sarcomere, the functional unit of skeletal muscle. Muscle contraction occurs when overlapping actin and myosin myofilaments overlap further and shorten the muscle cell. The myofilaments keep their length.