A special enzyme, acetylcholinesterase, breaks down the released acetylcholine so that it cannot continue to bind to the muscle membrane. In this way, the nerve controls the action of the muscle such that the muscle can only generate a current when the nerve has first generated a current. Two other proteins, troponin and tropomyosin, form a complex weave between the actin and myosin, and prevent contact. The shape of the myosin molecule is very complex. Actually, a globular head on myosin attaches to a long stalk on the major portion of the myosin molecule.
Numerous heads exist on a single myosin molecule.
This head is flexible and attaches to the actin molecule. The head allows for energy requiring movement of the actin molecule along the myosin molecule. It can be considered a ratchet because it detaches from the binding site on actin after the power stroke, goes back to its original orientation, and attaches to another binding site on actin, further down the molecule. This process slides the actin filament along the myosin filament and is known as the sliding filament theory of muscle contraction. It was initially proposed by A.F. Huxley in 1957.