Lourenço G, Iglesias C, Marchand-Pauvert V
INSERM, U731, Paris, F-75013, France.
Exp Brain Res. 2007 Apr;178(2):267-84. doi: 10.1007/s00221-006-0729-7. Epub 2006 Nov 8.
Effects of electrical stimulation of ulnar and median nerves at wrist level were investigated in post-stimulus time histograms (PSTHs) of single motor units from both flexors and extensors in human arm and forearm. Stimulation of ulnar nerve produced late (mean extra time-after monosynaptic group Ia excitation-10.7 +/- 0.1 ms) high-threshold (>1.2 x motor threshold, MT) excitation, which was not reproduced by purely cutaneous stimulation, in all the investigated motor nuclei except in Extensor Carpi Radialis. Stimulation of median nerve, and of the skin of fingers II and III (at palmar side level), produced short latency inhibition (mean extra time 3.8 +/- 0.3 ms), which was most often truncated or followed by late excitation (mean extra time 11.8 +/- 0.3 ms); both effects were of low threshold (0.8 x MT). Short latency inhibition was very strong, and late excitation was rare and weak in almost all the investigated motor units except in those supplying flexors in forearm, in which the main effect was the late facilitation (stronger than in other motoneurones). Since extra time was not more than 13 ms, it is suggested that the late effects may be mediated through spinal pathways, at least during their 3-5 first ms. Based on the electrophysiological results and on the anatomical characteristics of ulnar and median nerves, it is assumed that ulnar-induced late high-threshold peak in PSTHs might reflect group II excitation in spinal motoneurones, and median-induced modifications in motor unit discharge, mainly cutaneous control of motoneurone discharge. Since the central delay of median-induced inhibition is longer the more caudal the motoneurone, inhibitory propriospinal-like interneurones are supposed to mediate cutaneous inhibitory control from hand upon muscles in arm and forearm. Potential roles of proprioceptive and cutaneous control from hand to more proximal musculature, provided by ulnar and median nerve, respectively, during precise hand movements are discussed.
在人类手臂和前臂的屈肌和伸肌单运动单位的刺激后时间直方图（PSTH）中，研究了腕部尺神经和正中神经电刺激的效应。刺激尺神经会产生晚期（单突触Ia群兴奋后平均额外时间 - 10.7±0.1毫秒）高阈值（>1.2×运动阈值，MT）兴奋，除桡侧腕伸肌外，在所有研究的运动核中，这种兴奋不会由单纯的皮肤刺激产生。刺激正中神经以及手指II和III的皮肤（在手掌侧水平）会产生短潜伏期抑制（平均额外时间3.8±0.3毫秒），这种抑制最常被截断或随后出现晚期兴奋（平均额外时间11.8±0.3毫秒）；这两种效应都是低阈值（0.8×MT）。短潜伏期抑制非常强烈，在几乎所有研究的运动单位中，晚期兴奋都很少见且微弱，但在前臂屈肌的运动单位中除外，在这些单位中主要效应是晚期易化（比其他运动神经元更强）。由于额外时间不超过13毫秒，提示至少在最初的3 - 5毫秒内，晚期效应可能通过脊髓通路介导。基于电生理结果以及尺神经和正中神经的解剖学特征，推测尺神经在PSTH中诱导的晚期高阈值峰值可能反映脊髓运动神经元中的II群兴奋，而正中神经诱导的运动单位放电变化，主要是对运动神经元放电的皮肤控制。由于正中神经诱导的抑制的中枢延迟在运动神经元越靠尾端时越长，推测抑制性脊髓 propriospinal样中间神经元介导从手部到手臂和前臂肌肉的皮肤抑制控制。讨论了在精确手部运动过程中，分别由尺神经和正中神经提供的从手部到更近端肌肉组织的本体感觉和皮肤控制的潜在作用。
