Emonet-Dénand F, Laporte Y, Petit J
Laboratoire de Neurophysiologie, Collège de France, Paris, France.
J Neurophysiol. 1997 Mar;77(3):1425-31. doi: 10.1152/jn.1997.77.3.1425.
A study of the distribution in cat peroneus tertius spindles of 42 single static gamma-axons was recently carried out with a physiological method for identifying the intrafusal muscle fibers supplied by single gamma-axons. It was found that 35 axons (83%) supplied both slow-contracting bag2 fibers and fast-contracting chain fibers. The distribution of these axons generally varied from one spindle to another among all the spindles that each of them supplied (bag2 and chain fibers together, bag2 alone, chains alone). To find some functional consequences of this coactivation, responses of primary endings to sinusoidal stretch of the muscle (amplitude 0.5-1 mm, frequency linearly increasing from 0.6 to 8-9 Hz in 12 s) were recorded at different average muscle lengths (0.5, 1.0, and 1.5 mm shorter than maximal physiological length) in nembutalized cats during repetitive stimulation at 10, 20, and 30 Hz of single gamma-axons previously shown to supply bag2 and chain fibers in the spindles bearing the primary endings. These responses were compared with responses elicited in passive spindles and during activation of either bag2 fibers or chain fibers alone. Several records of discharge frequency were averaged. During stimulation at 30 Hz of gamma-axons coactivating bag2 and chain fibers, the averaged discharge of primary endings became continuous (that is, without interruption during each shortening phase as occurs in passive spindles) over the whole range of stretch frequencies. The modulation of the discharge was roughly sinusoidal, with an amplitude that increased with the stretch frequency. Stimulation at 30 Hz of gamma-axons activating bag2 fibers alone elicited a modulation of comparable shape and amplitude but only in the range of sinusoidal stretch from 0.6 to 3-4 Hz. Stimulation at 30 Hz of gamma-axons activating chain fibers alone elicited for each cycle in the range of 0.6 to 5-6 Hz a distorted modulation of large amplitude with a minimal frequency close to that of the stimulation. The average muscle length did not significantly influence these various responses. In summary, the coactivation of bag2 and chain fibers, at presumed physiological frequencies, enables primary endings to continuously signal changes of length over a large range of stretch velocities independently of the average muscle length.
最近采用一种生理学方法对42条单根静态γ运动轴突在猫第三腓骨肌肌梭中的分布进行了研究，该方法用于识别由单根γ运动轴突支配的梭内肌纤维。研究发现，35条轴突（83%）支配了慢收缩的袋状2型纤维和快收缩的链状纤维。在它们所支配的所有肌梭（袋状2型纤维和链状纤维一起、仅袋状2型纤维、仅链状纤维）中，这些轴突的分布通常因肌梭而异。为了探究这种共同激活的一些功能后果，在戊巴比妥麻醉的猫中，于不同的平均肌肉长度（比最大生理长度短0.5、1.0和1.5毫米）下，在10、20和30赫兹重复刺激先前已证明在含有初级终末的肌梭中支配袋状2型纤维和链状纤维的单根γ运动轴突时，记录初级终末对肌肉正弦拉伸（幅度0.5 - 1毫米，频率在12秒内从0.6线性增加至8 - 9赫兹）的反应。将这些反应与在被动肌梭以及单独激活袋状2型纤维或链状纤维时引发的反应进行比较。对多个放电频率记录进行了平均。在30赫兹刺激共同激活袋状2型纤维和链状纤维的γ运动轴突时，在整个拉伸频率范围内，初级终末的平均放电变得连续（即不像被动肌梭那样在每个缩短阶段有中断）。放电的调制大致呈正弦形，其幅度随拉伸频率增加。在30赫兹刺激仅激活袋状2型纤维的γ运动轴突时，仅在0.6至3 - 4赫兹的正弦拉伸范围内引发了具有类似形状和幅度的调制。在30赫兹刺激仅激活链状纤维的γ运动轴突时，在0.6至5 - 6赫兹范围内的每个周期引发了大振幅的扭曲调制，其最小频率接近刺激频率。平均肌肉长度对这些不同反应没有显著影响。总之，在假定的生理频率下，袋状2型纤维和链状纤维的共同激活使初级终末能够在很大范围的拉伸速度内独立于平均肌肉长度持续发出长度变化信号。
