Histological Studies on Correlation Between Function and Structure of Skeletal Muscle Part 3. Histological studies on correlation between function and structure of muscle spindle

1) By lipid and succinic dehydrogenase staining, it can be proved that muscle spindle (stretch receptor) consists of sarcosome rich (red) and sarcosome poor (pale) intrafusal fiber, which corresponds to the physiologically known 2 units, tonic (slow) and phasic (fast). 2) Muscle spindles can be classified into three types according to the histochemical type of intrafusal fibers. Type 1. Muscle spindle; consists of only red (tonic) intrafusal fibers Type 2. Muscle spindle; consists of only pale (phasic) intrafusal fibers Type 3. Muscle spindle; consists of both red and pale intrafusal fibers Proximal muscles of the extremity with tonic function many 1 and 3 types while in the distal mucles with phasic contraction 2 and 3 types are often seen 3) Spindle efferent nerves (γ-fiber) consists of relatively large (5-9μ) and small (3-5μ) nerve fibers. 4) Human muscle spindle like that of a cat is composed of two types of intrafusal fibers and is innervated by small (6μ) and large (16μ) nerve fibers. These findings show that γ-system may exist in the human body as in a cat.