Gregory J E, Proske U
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Int J Dev Neurosci. 1991;9(1):101-9. doi: 10.1016/0736-5748(91)90077-y.
In the lateral flexor digitorum longus muscle (FDL) of anaesthetized kittens aged 3-21 days, alpha (alpha) and gamma (gamma) motoneurone conduction velocities were measured together with motor unit tensions. Conduction velocity lay in the range 8-27 msec-1 for alpha motoneurones and 2-10 msec-1 for gamma motoneurones. Motor unit tetanic tensions were 3-47 mN with the largest units being 2-2.2% of whole muscle tension. The hypothesis was tested that motor axons conducting within the gamma range and presumed to be innervating the intrafusal fibres of muscle spindles, on stimulation, produced measurable tension. Stimulating gamma motoneurones in the adult produces no tension. The hypothesis was based on histological observations that while in the adult, intrafusal fibres were about one third of the size of extrafusal fibres, in kittens the two were nearly equal, both in length and diameter. It was shown by means of signal averaging during stimulation of ventral root filaments that whenever tension was recorded in the muscle an impulse could be detected in the muscle nerve conducting at alpha motoneurone tempo. It is concluded that in the kitten, despite the fact that intrafusal and extrafusal fibres are of similar size, stimulating single gamma motoneurones does not develop measurable tension.
在3至21日龄麻醉小猫的外侧趾长屈肌（FDL）中，测量了α（阿尔法）和γ（伽马）运动神经元的传导速度以及运动单位张力。α运动神经元的传导速度在8至27米/秒范围内，γ运动神经元的传导速度在2至10米/秒范围内。运动单位强直张力为3至47毫牛，最大的单位为整块肌肉张力的2%至2.2%。对以下假设进行了测试：传导速度在γ范围内且推测支配肌梭内肌纤维的运动轴突，在受到刺激时会产生可测量的张力。在成体中刺激γ运动神经元不会产生张力。该假设基于组织学观察结果，即在成体中，肌梭内肌纤维的大小约为梭外肌纤维的三分之一，而在小猫中，两者在长度和直径上几乎相等。通过在刺激腹根细丝时进行信号平均显示，每当在肌肉中记录到张力时，都能在以α运动神经元速度传导的肌肉神经中检测到一个冲动。得出的结论是，在小猫中，尽管肌梭内肌纤维和梭外肌纤维大小相似，但刺激单个γ运动神经元不会产生可测量的张力。
