Clarke A M, Michie P T, Glue L C
J Neurol Neurosurg Psychiatry. 1972 Apr;35(2):221-7. doi: 10.1136/jnnp.35.2.221.
The experiments reported in this paper tested the hypothesis that the afferent potential elicited by a tendon tap in an isometrically recorded phasic stretch reflex can be detected in the surface EMG of normal humans when appropriate techniques are used. These techniques involved (1) training the subjects to relax mentally and physically so that the EMG was silent before and immediately after the diphasic MAP which reflects a highly synchronous discharge of afferent impulses from low threshold muscle stretch receptors after a tendon tap, and (2) using a data retrieval computer to summate stimulus-locked potentials in the EMG over a series of 16 samples using taps of uniform peak force and duration on the Achilles tendon to elicit the tendon jerk in the calf muscles. A discrete, diphasic potential (A-wave') was recorded from EMG electrodes placed on the surface of the skin over the medial gastrocnemius muscle. The A-wave' afferent potential had the opposite polarity to the corresponding efferent MAP. Under control conditions of relaxation the A-wave' had a latency after the onset of the tap of 2 msec, the peak to peak amplitude was of the order of 5 μV and the duration was in the range of 6 to 10 msec. Further experiments were conducted to show that the A-wave' (1) was not an artefact of the instrumentation used, (2) had a threshold at low intensities of stimulation, and (3) could be reliably augmented by using a Jendrassik manoeuvre compared with the potential observed during control (relaxation) conditions. The results support the conclusion that the `A-wave' emanates from the pool of muscle spindles which discharges impulses along group Ia nerve fibres in response to the phasic stretch stimulus because the primary ending of the spindles is known to initiate the stretch reflex and the spindles can be sensitized by fusimotor impulses so that their threshold is lowered as a result of a Jendrassik manoeuvre. The finding has important implications for the investigation of the fusimotor system in intact man.
当采用适当技术时，在正常人体的表面肌电图中能够检测到等长记录的相位性牵张反射中肌腱叩击所引发的传入电位。这些技术包括：(1) 训练受试者在精神和身体上放松，以使在反映肌腱叩击后低阈值肌肉牵张感受器传入冲动高度同步发放的双相运动诱发电位（MAP）之前及之后立即，肌电图保持静息状态；(2) 使用数据检索计算机，对一系列16个样本的肌电图中刺激锁定电位进行求和，这些样本是通过对跟腱施加具有统一峰值力和持续时间的叩击来诱发小腿肌肉的肌腱反射。从置于腓肠肌内侧皮肤表面的肌电图电极记录到一个离散的双相电位（“A波”）。“A波”传入电位与相应的传出MAP极性相反。在放松的对照条件下，“A波”在叩击开始后2毫秒出现潜伏期，峰峰值幅度约为5微伏，持续时间在6至10毫秒范围内。进一步的实验表明，“A波”：(1) 不是所用仪器的伪迹；(2) 在低强度刺激时有阈值；(3) 与对照（放松）条件下观察到的电位相比，通过使用Jendrassik动作可使其可靠增强。结果支持以下结论：“A波”源自肌梭池，该肌梭池在相位性牵张刺激时沿Ia类神经纤维发放冲动，因为已知肌梭的初级末梢可引发牵张反射，并且肌梭可通过梭内肌运动冲动而敏感化，从而因Jendrassik动作使其阈值降低。这一发现对完整人体中梭内肌运动系统的研究具有重要意义。
