“Involvement of the endocannabinoid system in pathophysiological mechanisms responsible for spasticity has been demonstrated in animal models of MS…

Evidence indicates that the antispasticity effects of THC:CBD oromucosal spray (Sativex®) are associated with enhanced cortical long-term potentiation.

CB1 receptors, which are associated with movement, postural control, and pain and sensory perception, influence glutamatergic pathways.

THC:CBD oromucosal spray was shown to reverse motor cortex plasticity from long-term depression through long-term potentiation of synaptic transmission, thereby restoring, at least in part, effective corticospinal inputs to spinal circuits.”

http://www.ncbi.nlm.nih.gov/pubmed/25278116

http://www.thctotalhealthcare.com/category/multiple-sclerosis-ms/