Lamb A H
Department of Pathology, University of Western Australia, Nedlands.
Aust Paediatr J. 1988;24 Suppl 1:37-9.
The adult motor system is precisely connected, topographically and functionally. This order is reached during embryonic development through a sequence of mechanisms which increasingly resolve the adult patterns of connectivity. First is axon guidance, which gives rise to a pattern of axon outgrowth leading to an approximation of the adult projections. Second there is a period of motoneuron death, which eliminates motoneurons which have projected to inappropriate regions of the limb, and, it is conjectured, motoneurons which are functionally less well connected in terms of the behaviour of the whole system. Third there is a period of retraction of axon terminals which refines the pattern of connectivity from polyneuronal to mononeuronal innervation of the muscle fibres. The patterns of retraction may be determined by the same functional criteria as are used in the control of motoneuron death.
成人运动系统在拓扑结构和功能上精确连接。这种有序性在胚胎发育过程中通过一系列机制得以实现，这些机制逐渐形成成人的连接模式。首先是轴突导向，它导致轴突生长模式，使轴突生长接近成人的投射模式。其次是运动神经元死亡期，在此期间，投射到肢体不适当区域的运动神经元被清除，据推测，从整个系统的行为来看，功能连接较差的运动神经元也会被清除。第三是轴突终末回缩期，它将连接模式从多神经元对肌纤维的支配细化为单神经元支配。回缩模式可能由与控制运动神经元死亡相同的功能标准决定。
