These are the neurons that actually drive the muscle cells. There are five classes, designated as alpha ( -MNs), static beta ( s-MNs), dynamic beta ( d-MNs), static gamma ( s-MNs), and dynamic gamma ( d-MNs). The -MNs are the main drive neurons for the extrafusal muscle fibers, and hence are known as slow (S), fast-resistant to fatigue (FR), and fast-fatiguing (FF) skeleto-motoneurons. The -MNs...