Definition: Spasticity refers to a condition in which muscles are stiff and cannot be relaxed. Although it is usually caused by damage to the cerebellum (the part of the brain that controls voluntary movement), it can also be caused from damage to the nerves from the brain to the spinal cord. It may occur due to genetic conditions, injury, or autoimmune disorders. Spasticity can affect walking, movement, or speech and symptoms might include poor posture, muscle tightness, exaggerated deep tendon reflexes, and repetitive jerky movments.