Descending modulations of stretch reflex gain in arm muscle

据报道，比目鱼肌的H反射在站立时比坐着时要小。这可能是在这些不同的姿势下，通过下行路径调节比目鱼肌的伸展反射增益的结果。比目鱼肌伸展反射的增益在运动过程中也受到调节。导致这些变化的神经机制被认为涉及到脊髓运动神经元上Ia终末的突触前抑制的调制。虽然正常人的比目鱼肌H反射在站立时比坐着时要少，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。这一观察表明，与腿部肌肉相比，手臂和腿部肌肉中与姿势相关的伸展反射调节的机制不同。为了探索这一假说，我们研究了坐位和站立时比目鱼肌和腕屈肌(FCR)诱发的H反射的调制。17例正常人和10例偏瘫患者…更多的教师参与了这项研究。H反射没有背景肌电，以最大限度地减少肌肉传入反馈。还记录了比目鱼肌站立时的H反射和伴随的背景肌电。H反射的幅度表示为其在每个姿势的最大M反应的大小。在正常受试者中，站立时比目鱼肌H反射比坐姿时的H反射降低。当记录伴随着背景肌肉活动的站立时，观察到比目鱼肌H反射的不稳定变化。正常人坐位与站立时FCR的H反射变化规律不同。然而，在十分之八的偏瘫患者中，从痉挛侧记录的FCRH反射在站立时比坐着时增加。考虑到在没有背景肌电的情况下的反应，比目鱼肌和FCR之间与姿势相关的H反射调制的差异可能取决于它们各自的脊髓运动神经元池在下行控制方面的差异。在背景肌电信号存在的情况下，即随着肌肉传入反馈的增加，影响运动神经元兴奋性的肌肉传入和下行通路都会引起比目鱼肌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，从而导致这些H反射的增加。而这种调节是通过对Ia突触的突触前抑制来实现的，用D1法进行评估。这些结果表明，臂部和腿部肌肉对伸展反射增益的体位相关调制受到不同的下行控制对突触前抑制Ia突触的影响。较少

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