Excerpt from "What If?" - Movement Disorders Video from the Life in Motion Awareness Campaign

Introduction

The word spasm comes from the Greek work, spasmos, meaning to pull or drag. Spasticity is defined as an involuntary, velocity-dependent, increased resistance to stretch. This definition means that the amount of resistance to stretching is at least partly determined by the speed with which a spastic muscle is stretched. One factor that is thought to be related to spasticity is the stretch reflex. This reflex is important in coordinating normal movements in which muscles are contracted and relaxed and in keeping the muscle from stretching too far. Although the end result of spasticity is problems with the muscles, spasticity is actually a caused by an injury to a part of the central nervous system (the brain or spinal cord) that controls voluntary movements. The damage causes a change in the balance of signals between the nervous system and the muscles. This imbalance leads to increased activity (excitability) in the muscles.

	Overview of Muscles