Lemon Roger N
Department of Clinical and Movement Sciences, Queen Square Institute of Neurology, UCL, London WC1N 3BG, UK.
Brain Sci. 2021 May 12;11(5):619. doi: 10.3390/brainsci11050619.
Upper motoneurons (UMNs) in motor areas of the cerebral cortex influence spinal and cranial motor mechanisms through the corticospinal tract (CST) and through projections to brainstem motor pathways. The primate corticospinal system has a diverse cortical origin and a wide spectrum of fibre diameters, including large diameter fibres which are unique to humans and other large primates. Direct cortico-motoneuronal (CM) projections from the motor cortex to arm and hand motoneurons are a late evolutionary feature only present in dexterous primates and best developed in humans. CM projections are derived from a more restricted cortical territory ('new' M1, area 3a) and arise not only from corticospinal neurons with large, fast axons but also from those with relatively slow-conducting axons. During movement, corticospinal neurons are organised and recruited quite differently from 'lower' motoneurons. Accumulating evidence strongly implicates the corticospinal system in the early stages of ALS, with particular involvement of CM projections to distal limb muscles, but also to other muscle groups influenced by the CM system. There are important species differences in the organisation and function of the corticospinal system, and appropriate animal models are needed to understand disorders involving the human corticospinal system.
大脑皮质运动区的上运动神经元（UMNs）通过皮质脊髓束（CST）以及向脑干运动通路的投射来影响脊髓和颅部运动机制。灵长类动物的皮质脊髓系统具有多样的皮质起源和广泛的纤维直径范围，包括人类和其他大型灵长类动物特有的大直径纤维。从运动皮质到臂部和手部运动神经元的直接皮质 - 运动神经元（CM）投射是一种较晚出现的进化特征，仅存在于灵巧的灵长类动物中，在人类中最为发达。CM投射源自一个更受限的皮质区域（“新”M1，3a区），不仅来自具有大的、快速轴突的皮质脊髓神经元，也来自那些轴突传导相对较慢的神经元。在运动过程中，皮质脊髓神经元的组织和募集方式与“下”运动神经元有很大不同。越来越多的证据强烈表明皮质脊髓系统在肌萎缩侧索硬化症（ALS）的早期阶段起作用，特别是CM投射到远端肢体肌肉，也涉及受CM系统影响的其他肌肉群。皮质脊髓系统的组织和功能存在重要的物种差异，需要合适的动物模型来理解涉及人类皮质脊髓系统的疾病。
