CYTOLOGICAL FEATURES OF 3 FIBER TYPES IN HUMAN STRIATED MUSCLE

A histochemical and electron microscopic study of the cytological features of the fiber types in normal human intercostal muscle is presented. From observations on succinic dehydrogenase, Sudan staining, and by electron microscopy, the human striated muscle fibers can be divided into three types; red, white and intermediate fibers. On the basis of mitochondrial content and distribution, each fiber type is characterized as follows. 1) The size and the composition of mitochondrial chains among the myofibrillar spaces : large and long in the red, absent in the white and medium in the intermediate fiber. 2) The size and shape of bracelet-like mitochondria which encompass the myofibrils at each I-band tend to be plump and multiform in the red, but slender and elongated in the white and the intermediate fibers. 3) Deposits of mitochondria beneath the sarcolemma, which are numerous in the red, scarce in the white and moderate in the intermediate fiber. Attention has been further paid to the sarcoplasmic reticulum, lipid droplets and glycogen particles. © 1969, Tohoku University Medical Press. All rights reserved.