Murphy P R, Pearson K G, Stein R B
Department of Neuroscience, Medical School, University of Newcastle, Newcastle upon Tyne, NE2 4HH, UK.
J Physiol. 2002 Aug 1;542(Pt 3):939-49. doi: 10.1113/jphysiol.2001.013428.
In order to investigate the nature (i.e. static or dynamic) of fusimotor drive to the flexor hallucis longus (FHL) and flexor digitorum longus (FDL) muscles during locomotion we recorded Ia and group II muscle spindle afferent responses to sinusoidal stretch (0.25 and 1 mm amplitude, respectively, 4-5 Hz) in a decerebrate cat preparation. FHL Ia and group II afferents generally had increased discharge rates and decreased modulation to stretch throughout the step cycle, compared to rest, suggesting raised static gamma drive at all locomotor phases. Although the modulation of Ia afferents was reduced during locomotion, most (13 of 18) showed a clear increasing trend during homonymous muscle activity (extension). This was consistent with phasic dynamic gamma drive to FHL spindles linked with alpha drive. In agreement with previous reports, FHL gave a single burst of EMG activity during the step cycle while FDL alpha drive had two components. One was related to extension while the other comprised a brief burst around the end of this phase. Typically FDL Ia and group II afferents also had elevated firing rates and reduced modulation at all locomotor phases, again implicating static gamma drive. Half the afferents (seven Ia, three group II) showed increased discharge during extension, suggesting phasic static gamma drive. There was no gamma drive associated with the late FDL alpha burst. In conclusion, the gamma drives to FHL and FDL differed during locomotion. FHL, which has the alpha drive of a classic extensor, received gamma drive that closely resembled other extensors. The gamma drive of FDL, which exhibits both extensor and flexor alpha synergies, did not match either muscle type. These observations are compatible with the view that fusimotor drive varies in different muscles during locomotion according to the prevailing sensorimotor requirements.
为了研究在运动过程中，肌梭运动神经对拇长屈肌（FHL）和趾长屈肌（FDL）的驱动性质（即静态或动态），我们在去大脑猫的实验准备中记录了Ia和II类肌梭传入纤维对正弦拉伸（振幅分别为0.25和1毫米，频率4 - 5赫兹）的反应。与静息状态相比，FHL的Ia和II类传入纤维在整个步周期内通常放电率增加且对拉伸的调制减少，这表明在所有运动阶段静态γ驱动增强。尽管在运动过程中Ia传入纤维的调制减少，但大多数（18个中的13个）在同名肌肉活动（伸展）期间呈现明显的增加趋势。这与与α驱动相关的FHL肌梭的相位动态γ驱动一致。与先前的报道一致，FHL在步周期中发出单次肌电图活动爆发，而FDL的α驱动有两个成分。一个与伸展有关，另一个包括在该阶段结束时的短暂爆发。通常，FDL的Ia和II类传入纤维在所有运动阶段也具有升高的放电率和减少的调制，再次表明存在静态γ驱动。一半的传入纤维（七个Ia，三个II类）在伸展期间放电增加，表明存在相位静态γ驱动。没有与FDL后期α爆发相关的γ驱动。总之，在运动过程中，对FHL和FDL的γ驱动不同。具有经典伸肌α驱动的FHL接受的γ驱动与其他伸肌非常相似。表现出伸肌和屈肌α协同作用的FDL的γ驱动与两种肌肉类型都不匹配。这些观察结果与以下观点一致，即在运动过程中，根据主要的感觉运动需求，不同肌肉的肌梭运动神经驱动会有所不同。
