How are satellite cells activated?

Satellite cells are uninucleate cells that typically lie in a quiescent state wedged between the basal lamina and sarcolemma of muscle fibers. 

In case of injury to the muscle, the damaged myofibers, immune cells, and blood vessels generate a combination of signals that activate the satellite cells. On activation, the satellite cells proliferate, creating new cells to replace the damaged cells. A few cells are preserved and return to their original dormant state ready to be reused for regeneration when the need arises.