Durbaba R, Taylor A, Ellaway P H, Rawlinson S
Department of Sensorimotor Systems, Imperial College of London, UK.
J Physiol. 2003 Jul 1;550(Pt 1):263-78. doi: 10.1113/jphysiol.2002.031930.
Static gamma-motor activity is strongly modulated by a particular phase relationship to the cyclic movements of locomotion, and this has a profound effect on the firing patterns of muscle spindle afferents. Whilst primary afferents are affected by both static and dynamic gamma-motor output,secondary afferents are affected significantly only by the static system acting via the intrafusal bag2 and chain fibres. It is therefore important to know how fluctuating patterns of static gamma-motor activity affect secondary afferents and to relate this to the actions of bagt and chain fibres. We have studied the action of single static gamma axons on secondary afferents in cat hindlimb muscles. Various physiological methods were explored to identify which of the intrafusal muscle fibres were being activated in each case, including the use of random stimulation and ramp frequency stimulation. The effects were also recorded of I Hz sinusoidally frequency-modulated gamma-axon stimuli and the amplitude and phase of the resulting afferent modulation related to the involvement of the bag2 and chain fibres. It was found that bag2 fibres are effective in biasing the secondary discharge, but their modulating action is relatively weak and involves a marked phase lag. Chain fibres acting alone cause strong modulation with very little phase lag. Mixed bag2 and chain-fibre action is most effective in modulating afferent discharge and causes intermediate values of phase lag. The results are discussed in relation to the control of natural movements and it is concluded that an important function of the static gamma motor system is to provide a signal to sum algebraically with the length-related signal. The results do not suggest that it could also usefully control stretch sensitivity.
静态γ运动神经元活动受到与运动周期性动作特定相位关系的强烈调制，这对肌梭传入纤维的放电模式有深远影响。虽然初级传入纤维受到静态和动态γ运动输出的影响，但次级传入纤维仅受到通过梭内袋2纤维和链状纤维起作用的静态系统的显著影响。因此，了解静态γ运动神经元活动的波动模式如何影响次级传入纤维，并将其与袋2纤维和链状纤维的作用联系起来很重要。我们研究了猫后肢肌肉中单个静态γ轴突对次级传入纤维的作用。探索了各种生理方法来确定每种情况下哪些梭内肌纤维被激活，包括使用随机刺激和斜坡频率刺激。还记录了1赫兹正弦调频γ轴突刺激的效果以及与袋2纤维和链状纤维参与相关的传入调制的幅度和相位。发现袋2纤维在使次级放电产生偏差方面是有效的，但其调制作用相对较弱且存在明显的相位滞后。单独作用的链状纤维会引起强烈调制且相位滞后很小。袋2纤维和链状纤维的混合作用在调制传入放电方面最有效，并导致中间值的相位滞后。结合自然运动的控制对结果进行了讨论，并得出结论：静态γ运动系统的一个重要功能是提供一个信号，以便与长度相关信号进行代数求和。结果并不表明它还能有效地控制伸展敏感性。
