Thomas C K, Ross B H
The Miami Project to Cure Paralysis and Department of Neurological Surgery, University of Miami School of Medicine, Florida 33136, USA.
J Neurophysiol. 1997 May;77(5):2847-50. doi: 10.1152/jn.1997.77.5.2847.
Surface electromyograms (EMG) and force were recorded during repeated involuntary spasms of paralyzed triceps surae muscles of four men with chronic cervical spinal cord injury. The firing rates of 78 medial gastrocnemius (MG) motor units also were recorded intramuscularly with tungsten microelectrodes. Spasms typically involved a relatively rapid rise, then a more gradual fall in triceps surae EMG and torque. Motor unit firing rates either increased and then decreased with the spasm intensity (54%) or were relatively constant (26%), firing mainly at 2-10 Hz. The remaining units (20%) produced trains that included one or several doublets. Mean peak spasm firing rates were 18 +/- 9 Hz (mean +/- SD) for rate modulated units and 11 +/- 10 Hz for units with little or no rate modulation. Some motor units fired at rates comparable with those recorded previously during maximum voluntary contractions performed by intact subjects. Others fired at rates below the minimum usually seen when normal units are first recruited (< 6 Hz). Doublets (interspike interval < 10 ms) often repeated every 123-333 ms, or were interspersed in trains firing at low steady rates (< 11 Hz). This study shows that rate coding for many motor units appears to be similar whether descending motor input is intact or whether it has been reduced severely by spinal cord injury. In contrast, rate modulation in other units appears to depend mainly on voluntary motor commands.
在四名患有慢性颈脊髓损伤的男性瘫痪的小腿三头肌反复不自主痉挛期间，记录了表面肌电图（EMG）和力量。还使用钨微电极在肌肉内记录了78个腓肠肌内侧（MG）运动单位的放电频率。痉挛通常表现为小腿三头肌EMG和扭矩相对快速上升，然后逐渐下降。运动单位放电频率要么随着痉挛强度增加然后降低（54%），要么相对恒定（26%），主要以2 - 10Hz放电。其余单位（20%）产生的序列包括一个或几个双峰。对于频率调制单位，平均峰值痉挛放电频率为18±9Hz（平均值±标准差），对于几乎没有或没有频率调制的单位，为11±10Hz。一些运动单位的放电频率与之前完整受试者进行最大自主收缩时记录的频率相当。其他单位的放电频率低于正常单位首次募集时通常看到的最小值（<6Hz）。双峰（峰间间隔<10ms）通常每123 - 333ms重复一次，或穿插在以低稳定频率（<11Hz）放电的序列中。这项研究表明，无论下行运动输入是否完整，或者是否因脊髓损伤而严重减少，许多运动单位的频率编码似乎都是相似的。相比之下，其他单位的频率调制似乎主要取决于自主运动指令。
