What is the unit of a skeletal muscle fibre called, which is located between two Z lines?

The skeletal muscle fiber unit located between two Z lines is known as the sarcomere. A sarcomere is the basic contractile unit of muscle tissue and is responsible for the striated appearance of skeletal and cardiac muscle. Within a sarcomere, the actin and myosin filaments interact to facilitate muscle contraction through the sliding filament mechanism. The Z lines, or Z discs, mark the boundaries of each sarcomere and anchor the thin filaments (actin) while the thick filaments (myosin) fill the central region between the Z lines.

Understanding this structure is crucial for grasping how muscles generate force and movement. Each segment of myofibril, which is a bundle of sarcomeres, contributes to the overall contraction of the muscle fiber, but the individual sarcomeres are the functional units. In contrast, myofilaments refer specifically to the proteins, actin and myosin, that create the contraction. A muscle fiber, on the other hand, is a collection of myofibrils and encompasses multiple sarcomeres, but does not represent the individual unit defined by the space between two Z lines.