Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan.
Marunouchi Hospital, Matsumoto, Japan.
Physiol Rep. 2022 Aug;10(16):e15431. doi: 10.14814/phy2.15431.
The projection pattern of low-threshold afferents from the extensor carpi radialis (ECR) to motoneurons supplying intrinsic hand muscles was investigated using the post-stimulus time-histogram (PSTH) and electromyogram-averaging (EMG-A) methods. Electrical conditioning stimulation was applied to the radial nerve branch innervating the ECR. In the PSTH study, changes in the firing probability of single motor units following the stimulation were examined. An early and significant peak (facilitation) was induced in the motoneurons innervating the muscles, but the facilitation was induced infrequently. The central latency of the facilitation was equivalent to that of homonymous facilitation through monosynaptic path in the spinal cord. In the EMG-A study, changes in the rectified and averaged electromyograms following the conditioning stimulation were examined. An early and significant peak (facilitation) was also induced. The facilitation disappeared after withdrawal of the vibration to the ECR muscle belly. Cutaneous nerve stimulation overlaying ECR never induced such facilitation in the PSTH and EMG-A studies. These findings suggest that monosynaptic facilitation mediated by group Ia afferents of ECR to the motoneurons supplying intrinsic hand muscles exists in humans, but the connection seems to be weak. This weakness might allow manipulatory movements of the hand.
使用刺激后时间直方图 (PSTH) 和肌电图平均 (EMG-A) 方法研究了来自伸腕肌 (ECR) 的低阈值传入纤维向供应内在手部肌肉的运动神经元的投射模式。电刺激施加于支配 ECR 的桡神经分支。在 PSTH 研究中，检查了刺激后单个运动单位放电概率的变化。在支配肌肉的运动神经元中诱导出早期和显著的峰 (易化)，但易化诱导不频繁。易化的中枢潜伏期与脊髓中通过单突触通路的同名易化的潜伏期相当。在 EMG-A 研究中，检查了条件刺激后整流和平均肌电图的变化。也诱导出早期和显著的峰 (易化)。当从 ECR 肌腹撤回振动时，易化消失。在 PSTH 和 EMG-A 研究中，覆盖 ECR 的皮神经刺激从未诱导出这种易化。这些发现表明，ECR 的 Ia 传入纤维介导的对供应内在手部肌肉的运动神经元的单突触易化存在于人类中，但这种联系似乎很弱。这种弱点可能允许手部的操纵运动。
