Normal and denervated muscle: A morphometric study of fine structure

Morphometric studies demonstrated measurable differences in the fine structure of rat red and white muscle fibers in the normal state. The effects of denervation were observed over a period of 84 days. After denervation myofibrillar atrophy was proportionate to, or only slightly greater than, fiber size atrophy. There was both an absolute and relative increase in mitochondrial mass in the early stage of denervation. The absolute mitochondrial mass then decreased and became proportionate to fiber size. There was reorientation of mitochondria in space after denervation. Both an absolute as well as a relative increase of sarcotubular surface occurred soon after denervation. This was followed by an absolute decrease that was less than proportionate to fiber size atrophy so that the concentration of sarcotubules in a given fiber region was increased throughout the study. These morphometric methods can be used in investigating the pathologic reactions and physiologic adaptations of skeletal muscle.