Muscle is composed of small units known as myofibril which itself composed of cylindrical bundles of thread like filaments; thick filament and thin filament known as myosin and actin respectively.
These filaments make up a myofibril which is organized into a chain of contractile units called sarcomeres. . There are two more proteins known as titin and nebulin which also contribute to the structure of sarcomere.
The function of the muscle is to contract and these filaments play a major role in it