 The cause of spasticity is thought to be where an imbalance occurs in the excitatory and inhibitory input to α motor neurons caused by damage to the spinal cord and/or central nervous system.The damage causes a change in the balance of signals between the nervous system and the muscles, leading to increased excitability in muscles.This is common in people who have cerebral palsy, brain injuries or a spinal cord injury, but it can happen to anybody e.g.