Keen Douglas A, Fuglevand Andrew J
Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ 85721, USA.
J Neurophysiol. 2004 Jun;91(6):2515-23. doi: 10.1152/jn.01178.2003. Epub 2004 Jan 14.
A peculiar aspect of the muscular organization of the human hand is that the main flexors and extensors of the fingers are muscles that each give rise to four parallel tendons that insert on all the fingers. It has been hypothesized that these multi-tendoned muscles are comprised of functional compartments, with each finger controlled by a discrete population of motor units. The purpose of this study was to determine the force distribution across the four fingers for motor units in human extensor digitorum (ED), a multi-tendoned muscle that extends the fingers. The force distribution was assessed by spike-triggered averaging and intraneural microstimulation for 233 and 18 ED units, respectively. A selectivity index from 0 (force equally distributed across the fingers) to 1.0 (force concentrated on a single finger) was used to quantify the distribution of motor unit force across the four digits. The mean selectivity index was high for ED motor units assessed with intraneural microstimulation (0.90 +/- 0.28) and was significantly greater than that obtained with spike-triggered averaging (0.38 +/- 0.14). Therefore it is likely that each finger is acted on by ED through a discrete population of motor units and that weak synchrony between motor units in different compartments of ED may have contributed to the appearance of spike-triggered average force on multiple fingers. Moreover, the high selectivity of motor units for individual fingers may provide the mechanical substrate needed for highly fractionated movements of the human hand.
人类手部肌肉组织的一个独特之处在于，手指的主要屈肌和伸肌都是各自产生四条平行肌腱并附着于所有手指的肌肉。据推测，这些多肌腱肌肉由功能分区组成，每个手指由一组离散的运动单元控制。本研究的目的是确定人类指伸肌（ED）中运动单元在四个手指上的力分布，ED是一种伸展手指的多肌腱肌肉。分别通过触发脉冲平均法和神经内微刺激法对233个和18个ED运动单元的力分布进行了评估。使用从0（力在各手指间均匀分布）到1.0（力集中在单个手指上）的选择性指数来量化运动单元力在四个手指上的分布。通过神经内微刺激评估的ED运动单元的平均选择性指数较高（0.90±0.28），且显著大于通过触发脉冲平均法获得的指数（0.38±0.14）。因此，很可能ED通过一组离散的运动单元作用于每个手指，并且ED不同分区的运动单元之间微弱的同步性可能导致了在多个手指上出现触发脉冲平均力。此外，运动单元对单个手指的高选择性可能为人类手部高度精细的运动提供所需的机械基础。
