Every body movement, from raising a hand to smiling, involves a complex interaction between the central nervous system (brain and spinal cord), nerves, and muscles. Damage to or malfunction of any of these components may result in a movement disorder.
Different types of movement disorders can develop, depending on the nature and location of the damage or malfunction, as in the following:
Damage to the parts of the brain that control voluntary (intended) movement or the connections between the brain and spinal cord: Weakness or paralysis of the muscles involved in voluntary movements and exaggerated reflexes
Damage to the basal ganglia (collections of nerve cells located at the base of the cerebrum, deep within the brain): Involuntary (unintended) or decreased movements, but not weakness or changes in reflexes
Damage to the cerebellum: Loss of coordination
The basal ganglia help initiate and smooth out voluntary muscle movements, suppress involuntary movements, and coordinate changes in posture.
The cerebellum coordinates the body’s movements, helps the limbs move smoothly and accurately, and helps maintain balance.
Some movement disorders, such as hiccups, are temporary, usually causing little inconvenience. Others, such as Parkinson disease, are serious and progressive, impairing the ability to speak, use the hands, walk, and maintain balance when standing.
Locating the Basal Ganglia
The basal ganglia are collections of nerve cells located deep within the brain. They include the following:
The basal ganglia help initiate and smooth out muscle movements, suppress involuntary movements, and coordinate changes in posture. |
Classification
Classifying movement disorders often helps doctors identify the cause.
Movement disorders are commonly classified as those that cause
Decreased or slow movement
Increased movement
The most common disorder that decreases and/or slows movement is
Disorders that increase movement include
Akathisia (inability to sit still)
Stereotypies (stereotypic movements)
Stereotypies are repetitive, rhythmic movements. They occur in children with autism spectrum disorders, intellectual disability, or encephalitis, as well as in children without these conditions. These movements can usually be stopped by distracting the child—for example, by calling the child's name.
Coordination problems are sometimes classified as disorders that increase movement. They are often caused by malfunction of the cerebellum, resulting in tremor and problems with balance and walking.
In some disorders, movement is increased and decreased. For example, Parkinson disease causes tremors—increased unintended (involuntary) movements—and slow intended (voluntary) movements.
Disorders that increase movement can be
Rhythmic, which are primarily tremors (although tremors are sometimes irregular, as occurs in dystonia)
Nonrhythmic, which may involve slow or rapid movements and/or a sustained position
Some rapid, nonrhythmic movements, such as tics, can be temporarily stopped (suppressed). Others, such as hemiballismus, chorea, and myoclonus, may be difficult to suppress or impossible to suppress completely.
