Transverse sections of mouse skeletal muscles
Transverse sections of mouse skeletal muscles, with muscle fibers in red and their nuclei in blue. At the top, a non-injured muscle. The nuclei of the fibers are found at the periphery. The photograph at the bottom shows a regenerating muscle, 12 days after injury. Regenerating fibers have centrally located nuclei and many of them are smaller in size. The capacity of skeletal muscles to undergo regeneration depends on skeletal muscle stem cells, called myosatellite cells. Upon muscle injury, myosatellite cells undergo activation, proliferate, differentiate and fuse with each other to form new fibers.