A. Skeletal muscle 1. Muscles are attached at either end to tendons to exert a pull. The muscle fiber is the cellular unit. It is a syncytial elongated cell with many peripheral nuclei. The syncytial myofiber is formed in the embryo by the fusion of many myoblasts.
Satellite cells represent stem cells held in reserve.
Myofibrils are intracellular contractile cords, 1-2 m in diameter, running longitudinally within the muscle fiber. They are striated and it is the registration of adjacent myofibril striations that gives muscle its banded appearance. Contraction is predominantly voluntary. Individual muscle cells are each innervated which allows for graded strength in contraction by the recruitment of varying numbers of muscle cells. B. Cardiac muscle 1.