Jami L, Petit J, Scott J J
J Physiol. 1985 Dec;369:323-35. doi: 10.1113/jphysiol.1985.sp015904.
The discharges from primary and secondary spindle endings of the cat peroneus tertius muscle were recorded during stimulation of static skeletofusimotor (static beta) axons at frequencies comparable with the presumed range of motoneuronal firing rates. When stimulated at 20-40/s, static beta-axons exerted typical static actions on the spindles they innervated, including activation of primary endings with reduction of their dynamic sensitivity and activation of secondary endings. For these frequencies, the extrafusal portions of static beta-motor units developed unfused contractions producing oscillations of tension within the muscle. After suppression of extrafusal contractions, the effects of the stimulation of static beta-axons on spindle discharge could persist unaltered, showing that extrafusal events need not interfere with the specific intrafusal actions of static beta-axons. Stimulation of a static beta-axon at 20-40/s often elicited a response of primary endings in which the discharge exactly followed the stimulation frequency, i.e. it was driven 1:1. Purely mechanical excitation of a spindle by unfused extrafusal contractions could also drive its discharge at the stimulation frequency. The persistence of static beta-driving after suppression of extrafusal contraction provided evidence for its intrafusal origin. Driving elicited by static beta-axons could persist during changes in muscle length, but small fluctuations in the delay between each impulse and the preceding stimulus were observed. These fluctuations were clearly related to the changes in muscle length, indicating that although the primary ending discharge remained driven 1:1 at the stimulation frequency, the receptor was not totally insensitive to length changes.
在以与假定的运动神经元放电频率范围相当的频率刺激猫第三腓骨肌的静态骨胳肌梭运动（静态β）轴突时，记录了该肌初级和次级梭终末的放电情况。当以20 - 40次/秒的频率进行刺激时，静态β轴突对其支配的肌梭施加典型的静态作用，包括激活初级终末并降低其动态敏感性以及激活次级终末。对于这些频率，静态β运动单位的梭外部分产生不融合收缩，导致肌肉内张力振荡。在抑制梭外收缩后，刺激静态β轴突对肌梭放电的影响可能保持不变，这表明梭外事件不一定会干扰静态β轴突特定的梭内作用。以20 - 40次/秒的频率刺激静态β轴突时，常常会引发初级终末的反应，其中放电精确地跟随刺激频率，即呈1:1驱动。由不融合的梭外收缩对肌梭进行单纯的机械刺激也能以刺激频率驱动其放电。抑制梭外收缩后静态β驱动的持续存在为其梭内起源提供了证据。在肌肉长度变化期间，由静态β轴突引发的驱动可能持续存在，但在每个冲动与前一个刺激之间的延迟中观察到小的波动。这些波动显然与肌肉长度的变化有关，表明尽管初级终末放电在刺激频率下仍保持1:1驱动，但感受器并非对长度变化完全不敏感。
