Effects of postural threat on spinal stretch reflexes: evidence for increased muscle spindle sensitivity?
Effects of postural threat on spinal stretch reflexes: evidence for increased muscle spindle sensitivity?
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DOI：
10.1152/jn.00065.2013
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发表时间：
2013-08-01
影响因子：
2.5
通讯作者：
Carpenter, Mark G.
中科院分区：
文献类型：
--
作者：
Horslen, Brian C.;Murnaghan, Chantelle D.;Carpenter, Mark G.
站立平衡在日常生活中经常受到威胁。这些威胁通常包括坠落的可能性或后果高于正常水平的场景。当猫被置于这些场景中时，它们的反应是增加嵌在腿部肌肉中的肌肉纺锤波的敏感性，可能是为了增加神经系统可获得的与平衡相关的传入信息。目前，尚不清楚人类是否也通过改变肌肉纺锤体的敏感性来应对这种姿势威胁。在此，我们提出了两项研究，探讨了姿势威胁对脊柱拉伸反射的影响。在研究1中，我们通过让受试者站在抬高表面（3.2米）的边缘来控制与坠落增加的后果相关的威胁。在研究2中，我们通过偶尔倾斜被试站立的支撑面来增加摔倒的可能性，从而操纵威胁。在这两种情况下，我们使用Hoffmann (H)和肌腱拉伸(T)反射来探测比目鱼肌的脊髓拉伸反射回路。我们观察到，在两种威胁情景下，t反射振幅增加，h反射振幅不变。这些结果表明，脊髓拉伸反射的突触状态不受姿势威胁的影响，因此在t反射中激活的肌肉纺锤波在威胁条件下一定更敏感。我们认为，这种敏感性的增加可能是为了满足在受到威胁时限制运动的冲突需求，同时保持一定数量的与姿势控制相关的感觉信息。
Standing balance is often threatened in everyday life. These threats typically involve scenarios in which either the likelihood or the consequence of falling is higher than normal. When cats are placed in these scenarios they respond by increasing the sensitivity of muscle spindles imbedded in the leg muscles, presumably to increase balance-relevant afferent information available to the nervous system. At present, it is unknown whether humans also respond to such postural threats by altering muscle spindle sensitivity. Here we present two studies that probed the effects of postural threat on spinal stretch reflexes. In study 1 we manipulated the threat associated with an increased consequence of a fall by having subjects stand at the edge of an elevated surface (3.2 m). In study 2 we manipulated the threat by increasing the likelihood of a fall by occasionally tilting the support surface on which subjects stood. In both scenarios we used Hoffmann (H) and tendon stretch (T) reflexes to probe the spinal stretch reflex circuit of the soleus muscle. We observed increased T-reflex amplitudes and unchanged H-reflex amplitudes in both threat scenarios. These results suggest that the synaptic state of the spinal stretch reflex is unaffected by postural threat and that therefore the muscle spindles activated in the T-reflexes must be more sensitive in the threatening conditions. We propose that this increase in sensitivity may function to satisfy the conflicting needs to restrict movement with threat, while maintaining a certain amount of sensory information related to postural control.