Emonet-Dénand F, Laporte Y, Petit J
Laboratoire de Neurophysiologie, Collège de France, 75231 Paris Cedex 05, France.
J Neurophysiol. 1998 Jul;80(1):249-54. doi: 10.1152/jn.1998.80.1.249.
Static fusimotor innervation was compared in cat peroneus longus and tertius muscles because the gamma to spindle ratio is considerably higher in the longus (approximately 60 gamma axons for 17 spindles) than in the tertius (approximately 24 gamma axons for 14 spindles). Single gamma axons were identified as static (gamma(s)) by their typical effects on the response of primary ending to ramp stretch. The intrafusal muscle fibers that single gamma(s) axons activated in the spindles they supplied were identified by the features of cross-correlograms between Ia impulses and stimuli, at 100 Hz, and by those of primary ending responses during stimulation at 30 Hz. In each experiment, a large proportion of the gamma population was tested on about nine spindles. A statistical analysis was used to estimate the number of spindles supplied by single gamma(s) axons and the proportion of gamma(s) axons that supply only one spindle among those the stimulation of which had activated either bag2 or chain fibers alone in a single spindle. In peroneus longus, nearly all gamma(s) axons supply one or two spindles, whereas in peroneus tertius, the majority of gamma(s) axons supply from three to six spindles. The proportion of nonspecifically distributed gamma(s) axons, i.e., of axons that supply both bag2 fibers and chain fibers either in the same or in different spindles, is much lower (56%) in the longus than in the tertius (83%) as previously observed on a population of gammas axons that supplied from three to six spindles. Correspondingly, the proportion of specific axons is much higher in the longus (44%) than in the tertius (17%). In none of the two muscles was a strict relationship observed between the conduction velocity of gamma(s) axons and their intrafusal distribution (specific bag2, specific chain fibers, nonspecific). However, gamma(s) supplying bag2 fibers either specifically or in combination with chain fibers tended to have faster conduction velocities, which suggests that, in various motor acts, the proportion of activated bag2 and chain fibers may be related to the proportions of activated fast and slow gamma(s) axons.
对猫的腓骨长肌和第三腓骨肌的静态肌梭运动神经支配进行了比较，因为腓骨长肌中γ运动神经元与肌梭的比例（约17个肌梭对应60条γ运动轴突）比第三腓骨肌（约14个肌梭对应24条γ运动轴突）高得多。单个γ运动轴突通过其对初级终末对斜坡拉伸反应的典型影响被识别为静态γ运动轴突（γ(s)）。通过100Hz时Ia冲动与刺激之间的互相关图特征以及30Hz刺激时初级终末反应的特征，确定单个γ(s)运动轴突在其支配的肌梭中激活的梭内肌纤维。在每个实验中，对约九个肌梭上的大部分γ运动神经元群体进行了测试。采用统计分析来估计单个γ(s)运动轴突支配的肌梭数量，以及在单个肌梭中刺激时仅激活袋2纤维或链纤维的γ(s)运动轴突中仅支配一个肌梭的γ(s)运动轴突比例。在腓骨长肌中，几乎所有γ(s)运动轴突支配一或两个肌梭，而在第三腓骨肌中，大多数γ(s)运动轴突支配三到六个肌梭。如先前在支配三到六个肌梭的γ运动轴突群体中观察到的那样，非特异性分布的γ(s)运动轴突比例，即在同一或不同肌梭中同时支配袋2纤维和链纤维的轴突比例，在腓骨长肌中（56%）比第三腓骨肌中（83%）低得多。相应地，特异性轴突的比例在腓骨长肌中（44%）比第三腓骨肌中（17%）高得多。在这两块肌肉中，均未观察到γ(s)运动轴突的传导速度与其梭内分布（特异性袋2纤维、特异性链纤维、非特异性）之间存在严格关系。然而，特异性或与链纤维联合支配袋2纤维的γ(s)运动轴突往往具有更快的传导速度，这表明在各种运动行为中，激活的袋2纤维和链纤维的比例可能与激活的快γ(s)运动轴突和慢γ(s)运动轴突的比例有关。
