サイズ原理とレンショウ細胞に着目した筋張力制御の神経回路網モデル

抄録

A neural network model for control of the muscle force, consisting of motor cortex output cell, α-motoneurons, Renshaw cells and muscle units, was presented. Behaviors of the model were examined by digital computer simulations and compared with the physiological results obtained from human muscles (brachialis, extensor digitorum communis (EDC) and first dorsal interosseus muscle (FDI)). Obtained results are summarized below. 1) Firing rates of motor units vs. muscle force relations obtained from the model agreed with those observed in human muscles during voluntary isometric contractions. 2) Muscle force calculated by the model increased almost linearly with the discharge frequencies of a motor cortex output cell, consistent with the results observed in wrist or finger muscles of monkeys. The following suggestions were obtained in association with effects of the motoneuronal size or Renshaw cells' inhibition. 3) Orderly recruitment of motor units is predominantly influenced by the size of the α-motoneuron. 4) Difference in the firing rate vs. force relations among α-motoneurons of the one muscle can be mostly attributed to the difference in either the size of α-motoneurons or the gain between α-motoneuron and Renshaw cell. 5) Lower firing rates of motor units in EDC muscle can be attributed to the stronger inhibitory effects of Renshaw cells; the number of Renshaw cells of EDC muscle is large, or the Renshaw cells of EDC might be able to fire at higher rates. Weaker inhibitory effects of Renshaw cells may give rise to higher firing rates of FDI or brachialis muscles.