Descending modulations of stretch reflex gain in arm muscle

据报道，站立时比目鱼h反射比坐着时小。这可能是不同体位下下行通路调节比目鱼肌拉伸反射增益的结果。在运动过程中，比目鱼肌拉伸反射的增益也受到调节。这些变化的神经机制被认为与脊髓运动神经元突触前抑制Ia终端的调节有关。尽管正常受试者站立时比目鱼肌h反射比坐时少，但在痉挛患者中，临床上有时可以看到站立时手臂肌肉张力增加。这一观察结果表明，与腿部肌肉相比，手臂伸展反射的姿势相关调节机制不同。为了探究这一假说，我们分别检测了坐姿和站立时比目鱼肌和桡侧腕屈肌（FCR） h反射的调节。17例正常人和10例偏瘫患者参加了本研究。h反射没有背景肌电图，以尽量减少肌肉传入反馈。同时记录了比目鱼站立时的h反射和背景肌电图。h反射的振幅表示为每个姿势中最大m反应的大小。正常受试者站立时比目鱼肌h反射较无背景肌电图时坐着时减弱。当记录站立时伴随的背景肌肉活动时，观察到比目鱼h反射的不稳定变化。正常情况下，坐着和站着时，FCR中的h反射以不同的方式变化。然而，在十分之八的偏瘫患者中，从痉挛侧记录的FCR h反射在站立时比坐着时增加。考虑到在没有背景肌电图的情况下的反应，比目鱼肌和FCR之间姿势相关的h反射调节的差异可能取决于各自脊柱运动欧元池下降控制的差异。在背景肌电背景下，即肌肉传入反馈增强时，影响运动神经元兴奋性的肌肉传入和下行通路均引起比目鱼肌h -反射在坐姿和站立之间的不稳定变化。在偏瘫患者的痉挛侧，站立时对FCR的下行兴奋可能增加，导致这些h反射较正常受试者增加。这种调节是通过Ia突触的突触前抑制来实现的，用D1法评估。这些结果表明，手臂和腿部肌肉拉伸反射增益的姿势相关调节受到不同的下行控制对突触前抑制的Ia。少

It has been reported that the soleus H-reflex is smaller during standing than sitting. This could be the result of modulation the stretch reflex gain of soleus by descending pathways in these different postures. The gain of the soleus stretch reflex is also modulated during locomotion. The neural mechanism responsible for these changes is thought to involve modulation of presynaptic inhibition of Ia terminals on spinal motoneurons. Although the soleus H-reflex is less during standing than during sitting in normal subjects, in patients with spasticity, the arm muscle tone is sometimes seen clinically to increase during standing. This observation suggests that different mechanisms underlie the posture-related modulation of the stretch reflex in arm compared with leg muscles. To explore this hypothesis, we examined the modulation of H-reflexes evoked in both soleus and flexor carpi radialis (FCR) during sitting and standing respectively. Seventeen normal subjects and ten hemiplegic patien … More ts participated in this study. H-reflexes were without background EMG in order to minimise muscle afferent feedback. H-reflexes were also recorded during standing in the soleus with the accompanying background EMG. The amplitudes of H-refelxes were expressed as their size to the maximal M-response in each posture.In the normal subjects, soleus H-reflex were decreased during standing compared with sitting when no background EMG. When recorded during standing with the accompanying background muscle activity, unstable changes were observed in the soleus H-reflex. The H-reflex in FCR changed in a variable manner between sitting and standing in normals. However, in eight out of ten hemiplegic patients, the FCR H-reflexes recorded from the spastic side were increased during standing compared with sitting. Taking into account the responses in the absence of background EMG, the differences in posture-related modulations of H-reflex between soleus and FCR probably depend on differences in descending control of their respective spinal motoneuro pools. In the presence of background EMG, i.e., with increased muscle afferent feedback, both the muscle afferents and the descending patheway that affect motoneuron excitability caused unstable changes in soleus H-reflexes between sitting and standing. On the spastic side of the hemiplegic patients, the descending excitation to FCR is probably increased during standing which leads the increases in these H-reflexes compared with normal subjects. And this modulation is achieved by the presynaptic inhibition of Ia synapses, assessed by D1 method. These results suggest that posture-related modulation of stretch reflex gain in arm and leg muscles is subject to different descending control onto the presynaptic inhibition of Ia synapses. Less