Sacromere

Sarcomeres are the repeating sub-units that form the myofibrils. These myofibrils then, in turn, make up the muscle fibres, which form muscles. There are two kinds of sarcomeres, termed thick and thin. Hundreds of molecules of the protein myosin make up the thick units while actin is the primary component of the thin units. The thin units are approximately half the diameter of the thick units .