RELATIONS BETWEEN STRUCTURE AND FUNCTION IN THE DESIGN OF SKELETAL MUSCLES.

INTWORECENTLYPUBLISHED PAPERS (11,18)a detailedstudy wasmade of the properties of motor units in the soleus and medial gastrocenmius muscles of the cat. In particular, it was shown that there were great variations in the size of individual motor units and, paralleling them, important differences in their contractile characteristics. The full significance of these findings did not become apparent, however, until the observations reported in the preceding paper (7) had been made, indicating that the excitability of motoneurons is an inverse function of their size. From this it follows that the participation of a motor unit in graded motor activity is dictated by the size of its neuron. A corollary of this conclusion is that the total amount of contractile activity of a unit decreases as its size increases. These new findings on motor units have prompted a histochemical study of the soleus and m. gastrocnemius (MG), using recently developed methods (14) of staining muscle fibers for adenosine triphosphatase (ATPase). The results of this study are presented here. They provide a background for a functional analysis of the data on motor units. The hypotheses emerging from this analysis, in turn, offer a rationale for the histological findings. The conjunction of these different findings, all concerned with the same muscles, permits us to point out some previously unrecognized principles which govern the design of skeletal muscles.

[1]  D. Denny-Brown,et al.  On the Nature of Postural Reflexes , 1929 .

[2]  C. Sherrington,et al.  Numbers and Contraction-Values of Individual Motor-Units Examined in some Muscles of the Limb , 1930 .

[3]  H. S. Gasser,et al.  The classification of nerve fibers. , 1941 .

[4]  O. Meyerhof,et al.  Studies on adenosinetriphosphatase of muscle; a new magnesium-activated a denosinetriphosphatase. , 1948, The Journal of biological chemistry.

[5]  A. Hill.  The mechanics of voluntary muscle. , 1951, Lancet.

[6]  H J RALSTON.  Mechanics of voluntary muscle. , 1953, American journal of physical medicine.

[7]  M. Wachstein,et al.  Histochemistry of hepatic phosphatases of a physiologic pH; with special reference to the demonstration of bile canaliculi. , 1957, American journal of clinical pathology.

[8]  E. Henneman.  Relation between size of neurons and their susceptibility to discharge. , 1957, Science.

[9]  A. Novikoff,et al.  SURVIVAL OF LACTIC DEHYDROGENASE AND DPNH-DIAPHORASE ACTIVITIES AFTER FORMOL-CALCIUM FIXATION , 1958, The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society.

[10]  H. A. Padykula,et al.  A Histochemical Study of Normal and Denervated Red and White Muscles of the Rat , 1958, The Journal of biophysical and biochemical cytology.

[11]  I. A. Boyd.  The structure and innervation of the nuclear bag muscle fibre system and the nuclear chain muscle fibre system in mammalian muscle spindles , 1962, Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences.

[12]  H. A. Padykula,et al.  Histochemical classification of individual skeletal muscle fibers of the rat. , 1962, The American journal of anatomy.

[13]  H. A. Padykula,et al.  CYTOCHEMICAL STUDIES OF ADENOSINE TRIPHOSPHATASES IN SKELETAL MUSCLE FIBERS , 1963, The Journal of cell biology.

[14]  G. Vrbóva.  The effect of motoneurone activity on the speed of contraction of striated muscle , 1963, The Journal of physiology.

[15]  E. Henneman,et al.  PROPERTIES OF MOTOR UNITS IN A HETEROGENEOUS PALE MUSCLE (M. GASTROCNEMIUS) OF THE CAT. , 1965, Journal of neurophysiology.

[16]  G. Somjen,et al.  FUNCTIONAL SIGNIFICANCE OF CELL SIZE IN SPINAL MOTONEURONS. , 1965, Journal of neurophysiology.

[17]  E. Henneman,et al.  PROPERTIES OF MOTOR UNITS IN A HOMOGENEOUS RED MUSCLE (SOLEUS) OF THE CAT. , 1965, Journal of neurophysiology.