New Insights into the Function of the Corticospinal System in Health and Disease

Abstract

I will highlight a number of new findings about the organization and function of the corticospinal system which show it to be a multifunctional control system that has a rather different set of functions across different species. I will focus on corticospinal function in the primate.  The direct, cortico-motoneuronal system is found only in larger primates and is particularly well-developed in humans. Three other interrelated corticospinal features are specific to primates: the first is the presence of large, fast-conducting fibres that extend the range of corticospinal diameters from very small (~0.2 µm) to very large (>10 µm). The second is the presence of the fast K+ channel Kv3.1b in the soma and dendritic membrane of corticospinal neurons, and the third feature is very brief or ‘thin’ spikes, with a rapid recovery cycle, found in larger corticospinal neurons. Although these features provide primates, including humans, with an extremely versatile cortical control system, they also represent a serious vulnerability to trauma and disease, including spinal injury and ALS.