1. The discharge activity of muscle spindle endings located in tail and hind limb muscles was recorded during voluntary movements in the cat. 2. During active shortening of the receptor-bearing muscles, both primary and secondary endings tended to fall silent. This was more pronounced, the higher the rate of muscle shortening. We suggest that in unobstructed movements in which muscle velocities exceed 0.2 resting lengths per second (lr/sec), the firing patterns of spindle afferents are dominated by their responses to the length variations. At velocities lower than 0.2 lr/sec, fusimotor action may predominate. 3. When active muscle shortening was unexpectedly halted, both primary and secondary endings resumed firing, but the increases in discharge rate were not as abrupt as might have been expected had there been strong co-activation of fusimotor and skeletomotor neurones. Rather, for the types of movements studied, fusimotor action appears to have been quite modest.
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机译：1.在猫的自发运动中记录了位于尾巴和后肢肌肉中的纺锤体末端的放电活动。 2.在主动缩短带有受体的肌肉时，初级和次级末端均趋于沉默。肌肉缩短的速度越高，越明显。我们建议，在肌肉速度超过每秒0.2个静止长度（lr / sec）的无阻碍运动中，纺锤状传入球的发射模式主要取决于它们对长度变化的响应。在低于0.2 lr / sec的速度下，融合运动可能占主导地位。 3.当活动性肌肉缩短意外停止时，初级和次级末梢均恢复放电，但是如果融合运动和骨骼运动神经元强烈共激活，则放电速率的增加并不像预期的那样突然。相反，对于所研究的动作类型，自旋动作似乎相当适度。
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