Abstract

AV Hill’s paramount interest was of course in muscle function. Sherrington famously coined the phrase ‘To move things is all that mankind can do … for such the sole executant is muscle, whether in whispering a syllable or in felling a forest”. The close relationship between the cerebral cortex and movements of the hand is underlined by the presence of descending corticospinal fibres with direct cortico-motoneuronal (CM) connections, first described by Sherrington, that are particularly strong to the motoneurons supplying the thumb muscles. There is also a close relationship established by rapid somatosensory feedback pathways that brings tactile information from the glabrous skin of the hand to bear on motor cortex output neurons. This special sensorimotor relationship is of particular importance for skilled use of the hand as it engages in an enormous variety of technological and cultural activities, including tool manufacture and use. Although a motor cortex and corticospinal tract are highly conserved features of all mammalian brains, there are major species differences in the organisation of the cortex and its corticospinal projection. I shall discuss a number of interrelated features exhibited by the primate corticospinal system, which give some clues as to how a number of different functions might be mediated. The cortical control of the hand in the primate is particularly vulnerable to neurological disease, including stroke and spinal injury. In some forms of amyotrophic lateral sclerosis, the pattern of muscle weakness and wasting closely follows the distribution of CM projections, suggesting that such forms are a primate-specific disease that may be spread through CM connections.