Lateva Zoia C, McGill Kevin C
Rehabilitation Research and Development Center, VA Palo Alto Health Care System, Palo Alto, CA 94304, USA.
Clin Neurophysiol. 2007 Dec;118(12):2612-9. doi: 10.1016/j.clinph.2007.09.058. Epub 2007 Oct 31.
Motor-unit action potentials (MUAPs) with unstable satellite (late-latency) components are found in EMG signals from the brachioradialis muscles of normal subjects. We analyzed the morphology and blocking behavior of these MUAPs to determine their anatomical origin.
EMG signals were recorded from the brachioradialis muscles of 5 normal subjects during moderate-level isometric contractions. MUAP waveforms, discharge patterns, and blocking were determined using computer-aided EMG decomposition.
Twelve MUAPs with unstable satellite potentials were detected, always two together in the same signal. Each MUAP also had a second unstable component associated with its main spike. The blocking behavior of the unstable components depended on how close together the two MUAPs were when they discharged.
The latencies and blocking behavior indicate that the unstable components came from branched muscle fibers innervated by two different motoneurons. The satellite potentials were due to action potentials that traveled to the branching point along one branch and back along the other. The blockings were due to action-potential collisions when both motoneurons discharged close together in time.
Animal studies suggest that branched muscle fibers may be a normal characteristic of series-fibered muscles. This study adds to our understanding of these muscles in humans.
在正常受试者肱桡肌的肌电图（EMG）信号中发现了具有不稳定卫星（晚潜伏期）成分的运动单位动作电位（MUAPs）。我们分析了这些MUAPs的形态和阻滞行为，以确定其解剖学起源。
在中等强度等长收缩期间，记录5名正常受试者肱桡肌的EMG信号。使用计算机辅助EMG分解确定MUAP波形、放电模式和阻滞情况。
检测到12个具有不稳定卫星电位的MUAPs，总是在同一信号中两个一起出现。每个MUAP在其主波峰处还伴有第二个不稳定成分。不稳定成分的阻滞行为取决于两个MUAP放电时彼此的接近程度。
潜伏期和阻滞行为表明，不稳定成分来自由两个不同运动神经元支配的分支肌纤维。卫星电位是由于动作电位沿一个分支传导至分支点，再沿另一个分支返回所致。阻滞是由于两个运动神经元在时间上接近放电时发生动作电位碰撞所致。
动物研究表明，分支肌纤维可能是串联纤维肌肉的正常特征。本研究增进了我们对人类这些肌肉的了解。
