Fallon James B, Bent Leah R, McNulty Penelope A, Macefield Vaughan G
Prince of Wales Medical Research Institute, Sydney, New South Wales, Australia.
J Neurophysiol. 2005 Dec;94(6):3795-804. doi: 10.1152/jn.00359.2005. Epub 2005 Aug 3.
It has been known for some time that populations of cutaneous and muscle afferents can provide short-latency facilitation of motoneuron pools. Recently, it has been shown that the input from individual low-threshold mechanoreceptors in the glabrous skin of the hand can modulate ongoing activity in muscles acting on the fingers via spinally mediated pathways. We have extended this work to examine whether such strong synaptic coupling exists between tactile afferents in the sole of the foot and motoneurons supplying muscles that act about the ankle. We recorded from 53 low-threshold mechanoreceptors in the glabrous skin of the foot via microelectrodes inserted percutaneously into the tibial nerve of awake human subjects. Reflex modulation of ongoing whole muscle electromyography (EMG) was observed for each of the four classes of low-threshold cutaneous mechanoreceptors (17 of 21 rapidly adapting type I; 2 of 4 rapidly adapting type II; 7 of 18 slowly adapting type I; and 4 of 10 slowly adapting type II). Reflex modulation of the firing probability in single motor units (5 of 11) was also observed. These results indicate that strong synaptic coupling between tactile afferents and spinal motoneurons is not a specialization of the hand and emphasizes the potential importance of cutaneous inputs from the sole of the foot in the control of gait and posture.
一段时间以来，人们已经知道皮肤和肌肉传入神经群体可以对运动神经元池提供短潜伏期易化作用。最近，研究表明，手部无毛皮肤中单个低阈值机械感受器的输入可以通过脊髓介导的通路调节作用于手指的肌肉的持续活动。我们扩展了这项工作，以研究足底的触觉传入神经与支配踝关节周围肌肉的运动神经元之间是否存在如此强的突触耦合。我们通过经皮插入清醒人类受试者胫神经的微电极，记录了足部无毛皮肤中的53个低阈值机械感受器的活动。在四类低阈值皮肤机械感受器中的每一类中，均观察到了对持续的整块肌肉肌电图（EMG）的反射调制（21个快速适应I型中的17个；4个快速适应II型中的2个；18个缓慢适应I型中的7个；10个缓慢适应II型中的4个）。还观察到了对单个运动单位放电概率的反射调制（11个中的5个）。这些结果表明，触觉传入神经与脊髓运动神经元之间的强突触耦合并非手部所特有，并强调了足底皮肤输入在步态和姿势控制中的潜在重要性。
