Stevenson Andrew J T, Kamavuako Ernest N, Geertsen Svend S, Farina Dario, Mrachacz-Kersting Natalie
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, Aalborg, Denmark.
Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark.
J Physiol. 2015 Aug 15;593(16):3657-71. doi: 10.1113/JP270422.
The present study is the first to show short-latency crossed-spinal reflexes in the human upper leg muscles following mechanical rotations to the ipsilateral knee (iKnee) joint. The short-latency reflex in the contralateral biceps femoris (cBF) was inhibitory following iKnee extension perturbations, and facilitatory following iKnee flexion perturbations. The onset latency was 44 ms, indicating that purely spinal pathways mediate the cBF reflexes. The short-latency cBF inhibitory and facilitatory reflexes followed the automatic gain control principle, becoming larger as the level of background contraction in the cBF increased. The short-latency cBF reflexes were observed at the motor unit level using i.m. electromyography recordings, and the same population of cBF motor units that was inhibited following iKnee extensions was facilitated following iKnee flexions. Parallel interneuronal pathways from ipsilateral afferents to common motoneurons in the contralateral leg can therefore probably explain the perturbation direction-dependent reversal in the sign of the short-latency cBF reflex.
Interlimb reflexes contribute to the central neural co-ordination between different limbs in both humans and animals. Although commissural interneurons have only been directly identified in animals, spinally-mediated interlimb reflexes have been discovered in a number of human lower limb muscles, indicating their existence in humans. The present study aimed to investigate whether short-latency crossed-spinal reflexes are present in the contralateral biceps femoris (cBF) muscle following ipsilateral knee (iKnee) joint rotations during a sitting task, where participants maintained a slight pre-contraction in the cBF. Following iKnee extension joint rotations, an inhibitory reflex was observed in the surface electromyographic (EMG) activity of the cBF, whereas a facilitatory reflex was observed in the cBF following iKnee flexion joint rotations. The onset latency of both cBF reflexes was 44 ms, which is too fast for a transcortical pathway to contribute. The cBF inhibitory and facilitatory reflexes followed the automatic gain control principle, with the size of the response increasing as the level of background pre-contraction in the cBF muscle increased. In addition to the surface EMG, both short-latency inhibitory and facilitatory cBF reflexes were recorded directly at the motor unit level by i.m. EMG, and the same population of cBF motor units that were inhibited following iKnee extension joint rotations were facilitated following iKnee flexion joint rotations. Therefore, parallel interneuronal pathways (probably involving commissural interneurons) from ipsilateral afferents to common motoneurons in the contralateral leg can probably explain the perturbation direction-dependent reversal in the sign of the short-latency cBF reflex.
本研究首次表明，在对同侧膝关节（iKnee）进行机械旋转后，人大腿上部肌肉中出现了短潜伏期的交叉脊髓反射。在iKnee伸展性扰动后，对侧股二头肌（cBF）中的短潜伏期反射具有抑制作用，而在iKnee屈曲性扰动后则具有易化作用。起始潜伏期为44毫秒，表明纯粹的脊髓通路介导了cBF反射。cBF的短潜伏期抑制性和易化性反射遵循自动增益控制原则，随着cBF中背景收缩水平的增加而变大。使用肌内肌电图记录在运动单位水平观察到了cBF的短潜伏期反射，并且在iKnee伸展后被抑制的同一群cBF运动单位在iKnee屈曲后得到了易化。因此，从同侧传入神经到对侧腿部共同运动神经元的平行中间神经元通路可能解释了cBF短潜伏期反射信号中与扰动方向相关的反转。
肢体间反射有助于人类和动物不同肢体之间的中枢神经协调。虽然连合中间神经元仅在动物中被直接识别，但在人类的一些下肢肌肉中发现了脊髓介导的肢体间反射，这表明它们在人类中也存在。本研究旨在调查在坐姿任务中，当参与者在cBF中保持轻微的预收缩时，同侧膝关节（iKnee）旋转后，对侧股二头肌（cBF）肌肉中是否存在短潜伏期的交叉脊髓反射。在iKnee伸展关节旋转后，在cBF的表面肌电图（EMG）活动中观察到抑制性反射，而在iKnee屈曲关节旋转后，在cBF中观察到易化性反射。两种cBF反射的起始潜伏期均为44毫秒，对于经皮质通路来说太快而无法起作用。cBF的抑制性和易化性反射遵循自动增益控制原则，随着cBF肌肉中背景预收缩水平的增加，反应大小也增加。除了表面EMG外，还通过肌内EMG在运动单位水平直接记录了cBF的短潜伏期抑制性和易化性反射，并且在iKnee伸展关节旋转后被抑制的同一群cBF运动单位在iKnee屈曲关节旋转后得到了易化。因此，从同侧传入神经到对侧腿部共同运动神经元的平行中间神经元通路（可能涉及连合中间神经元）可能解释了cBF短潜伏期反射信号中与扰动方向相关的反转。
