Mrachacz-Kersting N, Grey M J, Sinkjaer T
Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, Aalborg DK 9220, Denmark.
Exp Brain Res. 2006 Jan;168(4):529-40. doi: 10.1007/s00221-005-0120-0. Epub 2005 Oct 21.
In sitting humans a rapid unexpected lengthening of the knee extensors elicits a stretch reflex (SR) response as recorded by the electromyogram (EMG) which comprises multiple bursts. These are termed short latency responses (SLR), medium latency responses (MLR) and long latency responses (LLR). The aim of this study was to determine if a transcortical pathway contributes to any of these bursts. Flexion perturbations (amplitude =4 degrees, velocity=150 degrees/s) were imposed on the right knee joint of sitting subjects (n=11). The effect of the perturbation on the electromyographic (EMG) response of the pre-contracted quadriceps muscle to magnetic stimulation of the contralateral motor cortex was quantified. Transcranial magnetic stimulation (TMS) was applied to elicit a compound motor evoked potential (MEP) in the target muscle rectus femoris (RF), in the vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF). The MEP and SR were elicited either in combination or separately. When applied in combination the delay between the SR and the MEP varied from 0 to 150 ms in steps of 4, 5 and 10 ms. Somatosensory evoked potentials (SEPs) were recorded from four subjects during the imposed stretch to quantify the latency of the resulting afferent volley. Onset latencies of responses in RF were 25+/-2 ms for the SR and 20+/-4 ms for the MEP. The average SEP latency was 24+/-2 ms. A transcortical pathway thus has the potential to contribute to the RF SR no earlier than 54+/-6 ms (SEP + MEP + 10 ms central processing delay) following the stretch onset. The duration of the total reflex burst was 85+/-6 ms. Significant facilitation of the MEP commenced at 78 ms, coinciding with the LLR component of the stretch response. No such facilitation was observed in the synergists VL and VM, or in the antagonist BF. Our results indicate that the LLR of the RF likely involves supraspinal pathways. More importantly, of the investigated muscles, this involvement of higher centers in the shaping of the LLR is specific to the RF muscle during the investigated task.
在坐姿的人体中，膝伸肌的快速意外拉长会引发一种牵张反射（SR）反应，通过肌电图（EMG）记录下来，该反应包含多个爆发波。这些爆发波被称为短潜伏期反应（SLR）、中潜伏期反应（MLR）和长潜伏期反应（LLR）。本研究的目的是确定经皮质通路是否对这些爆发波中的任何一个有贡献。对坐姿受试者（n = 11）的右膝关节施加屈曲扰动（幅度 = 4度，速度 = 150度/秒）。量化了该扰动对预先收缩的股四头肌在对侧运动皮质磁刺激下的肌电图（EMG）反应的影响。应用经颅磁刺激（TMS）在目标肌肉股直肌（RF）、股外侧肌（VL）、股内侧肌（VM）和股二头肌（BF）中诱发复合运动诱发电位（MEP）。MEP和SR可以联合诱发或单独诱发。联合应用时，SR和MEP之间的延迟以4、5和10毫秒的步长在0至150毫秒之间变化。在施加牵张过程中，从四名受试者记录体感诱发电位（SEP），以量化产生的传入冲动的潜伏期。RF中反应的起始潜伏期，SR为25±2毫秒，MEP为20±4毫秒。平均SEP潜伏期为24±2毫秒。因此，经皮质通路在牵张开始后不早于54±6毫秒（SEP + MEP + 10毫秒中枢处理延迟）对RF SR有贡献的可能性。总反射爆发的持续时间为85±6毫秒。MEP的显著易化在78毫秒开始，与牵张反应的LLR成分一致。在协同肌VL和VM或拮抗肌BF中未观察到这种易化。我们的结果表明，RF的LLR可能涉及脊髓上通路。更重要的是，在所研究的肌肉中，在研究任务期间，高级中枢对LLR形成的这种参与特定于RF肌肉。
