Mechanism of Muscle Contraction

The sliding filament theory, proposed by H.E. Huxley and A.F. Huxley, is also known as the walk-along theory or ratchet theory. It states that the interaction between actin and myosin filaments is the basic cause of muscular contraction: the actin filaments are interdigitated with the myosin filaments, rather like the crossed fingers of two clasped hands.

The head of the myosin molecule is joined to the actin backbone by a cross bridge that behaves like a hinge joint, so the head can tilt forward and backward but cannot tilt sideways. This tilting is an active process that requires the use of ATP — the myosin head itself carries ATPase activity, so it can derive energy from the breakdown of an ATP molecule, and this energy powers the movement of the head. …