Ljubisavljević M, Anastasijević R
Institute for Medical Research, Beograd, Yugoslavia.
Neuroscience. 1994 Nov;63(1):339-48. doi: 10.1016/0306-4522(94)90028-0.
Changes in discharge rate and responsiveness of muscle spindle afferents from triceps surae muscles were studied during long-lasting fatigue isometric contractions of either medial gastrocnemius or lateral gastrocnemius and soleus muscles in decerebrate cats. The rest of the hind limb was either denervated or its innervation was preserved. In denervated preparations a long-lasting post-contraction increase in discharge rate developed in the majority of primary (15 of 18) and in all (20) secondary afferents. This increase was abolished, while the decrease during muscle contraction was enhanced after application of procaine to the corresponding muscle nerve, to block either the small-diameter afferents from the contracting muscle or the fusimotor axons to the spindle of origin of the afferent recorded. In innervated preparations the long-lasting increase was replaced in the majority of primary endings (14 of 22) by a sharp burst at the end of muscle contraction, while in secondary afferents it was either absent or shorter-lasting than in denervated preparations. Changes in responsiveness to sinusoidal muscle length changes, indicating influences of both static and dynamic fusimotor neurons, were, however, similar in innervated and denervated preparations. The results obtained provide evidence that changes in muscle spindle outflow and responsiveness are elicited by the reflex increase in fusimotor activity developing in response to the fatigue-induced afferent discharges from the contracting muscle. Concomitant afferent inflow of another origin to fusimotor neurons affects the changes in spindle outflow, but not in responsiveness. In this way an appropriate increase in support to skeletomotor activity as well as in information on the fatigued muscle of higher motor centres, initiated by the fatigue itself, could be achieved through the gamma loop.
在去大脑猫的腓肠肌内侧头或外侧头及比目鱼肌进行长时间疲劳性等长收缩期间，研究了腓肠肌肌梭传入纤维的放电率和反应性变化。后肢的其余部分要么去神经支配，要么保留其神经支配。在去神经支配的标本中，大多数初级传入纤维（18根中的15根）和所有次级传入纤维（20根）在收缩后出现了放电率的持久增加。在向相应的肌肉神经施加普鲁卡因以阻断来自收缩肌肉的小直径传入纤维或记录传入纤维的肌梭起源处的梭内肌运动轴突后，这种增加被消除，而肌肉收缩期间的放电率下降则增强。在有神经支配的标本中，大多数初级终末（22根中的14根）在肌肉收缩结束时被尖锐的放电爆发所取代，而在次级传入纤维中，这种增加要么不存在，要么比去神经支配的标本持续时间短。然而，在有神经支配和去神经支配的标本中，对正弦肌肉长度变化的反应性变化（表明静态和动态梭内肌运动神经元的影响）是相似的。所获得的结果提供了证据，表明肌肉梭传出和反应性的变化是由因收缩肌肉疲劳诱导的传入放电而产生的梭内肌运动活动的反射性增加所引起的。来自其他来源的传入纤维对梭内肌运动神经元的同时传入影响了梭传出的变化，但不影响反应性。通过这种方式，由疲劳本身引发的对骨骼运动活动的适当支持增加以及向高级运动中枢提供的关于疲劳肌肉的信息增加，可以通过γ环路实现。
