FIGURE 2.

(A) SC niche: SCs lie between the sarcolemma of their associated myofiber and the surrounding basal lamina of the extracellular matrix. (B) SC activation: SCs remain in a quiescent state until activated by a number of stimuli, such as injury. The SCs are considered bona fide adult stem cells in that they self-renew to maintain the SC pool and are able to create myogenic tissue, that is, muscle progenitors, throughout the lifespan. (C) Peak activation of various cell types for repair: various nonmyogenic and myogenic cells act in a coordinated fashion to ensure appropriate repair. Abbreviation: SC, satellite cell.