Why & how does spasticity develop?

Spasticity is one of several clinical features/motor behaviors that may result following damage to the part of the brain or spinal cord involved in controlling voluntary movement. Collectively, these features are known as the upper motor neuron (UMN) syndrome. Spasticity is associated with a pathologically increased muscle tone. This creates stiffness and resistance to passive movement (the word ‘spasm’ originates from the Greek word, ‘spasmos’, which means to drag or pull). This change in muscle tone may increase the disability related to the disease at the origin of spasticity.