The basic contractile unit of a muscle fiber, consisting of actin and myosin. A structural unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band. A Sarcomere is the basic contractile unit of muscle fiber. Each Sarcomere is composed of two main protein filaments—actin and myosin—which are the active structures responsible for muscular contraction. The most popular model that describes muscular contraction is called the sliding filament theory.
