The histological features of striped muscle in relation to its functional activity

Abstract

The author has investigated the widely prevalent view that there is a close relation between rapidity or slowness of contraction and such histological features as redness or paleness, darkness or clearness, thickness or thinness, respectively, of individual fibers of a muscle; no such relation seems to exist. In mammalian muscle groups, fibers of markedly different speed of contraction may be arranged in distinct muscles {e.g., gastrocnemius and soleus) or they may form distinct "heads" within a single muscle (e.g., internal short head of triceps). The deeper heads are the more slowly contracting. Although the fibers within such a single head all have similar speeds of contraction, their histological features may vary vastly. In emaciated muscles granulation seems to vanish, leaving speed of contraction unchanged. In the new-born animal the fibers are granular and of slow contraction rate; with growth they become less granular and more rapid, but there is no relation between the 2 phenomena, since speed of contraction may be unaltered in a fattened animal, the fibers becoming, however, more granular. Griitzner''s theory that muscles of higher animals are composed of an intimate mixture of slow and rapid fibers is therefore untenable. The frequent occurrence of redness and slowness of contraction in the same muscle seems to be not a necessary but a chance event, since some rapid muscles may be red.