Spasticity, a disorder of muscle tone with its origin within the central nervous system, is usually a major component of cerebral palsy. It manifests as a velocity-dependent increase in tonic stretch reflex.

Patients with spasticity show increased resistance to passive limb motion.

Clinical characteristics of spasticity include the following:

• Hypertonia
• Clonus
• Crossed adductor reflexes
• Cocontraction of agonist and antagonist muscles is a major problem. 

Symptoms of the upper motoneuron syndrome can be divided into positive and negative categories:

• Positive symptoms include spasticity and released flexor reflexes
• Negative symptoms include loss of finger dexterity, weakness and loss of selective control of muscles and limb segments. 

Ref: Mayer NH. Clinicophysiologic concepts of spasticity and motor dysfunction in adults with an upper motoneuron lesion. Muscle Nerve 1997;20(suppl 6):S1-S13.