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Cerebral Palsy and the Basics of Movement.

Cerebral palsy is a group of impairments whose common thread is an "insult," or injury, to the developing brain. The injury occurs in the womb or soon after birth. Damage is not progressive (it does not continuously worsen), but the manner in which it expresses itself may change as a child matures and attempts to develop new skills. Often the effect is on a child's movement, one of the basic functions of the central nervous system.

The central nervous system (CNS) is truly extraordinary. It continuously performs many complex functions without you even having to "think" about it. To understand why children with cerebral palsy have the problems they have, it is necessary to learn a little about the way the brain--through the CNS--coordinates movement.

Go ahead, close your eyes and scratch your nose. Now think about the individual movements you just made. Think of the information your brain had to receive from sensors in your hand. Think about which muscles had to contract and which had to relax--in a very smooth, coordinated fashion--to get your finger to scratch your nose. You did not consciously think about how to move or how to find your nose. You did not worry about the pressure or speed of the arm, hand, or finger contraction; or the direction in which they moved. Your CNS did it all for you--in less than a second and without a second thought on your part!

Now imagine a child whose spastic cerebral palsy affects his or her arms trying to do the stone action. The movements would be stiff and jerky. There would be no "fine control" of the finger movements. Furthermore, with spasticity that is significant, the hand would not even open, nor would the arm extend.

Why is the movement so stiff? Why is the hand flexed shut? Why does one hand perform better than the other? The answer lies in following the signal from the brain to the muscles in the arm.

From brain to muscle

The motor system has several parts, each with a specific assignment to move the finger to the nose. The command starts at the top of the brain in the cerebral cortex, also called "the gray matter." The gray matter is made up of nerve cell bodies. These cell bodies receive instructions from other areas of the brain. In this case, it receives the message from the nose that it needs to be scratched.

The nerves in the brain for movement, called upper motor nerves (UMNs), are grouped together along a strip of brain referred to as "the motor strip" (See Illustration 1). Them, the nerves are all organized by group: the legs, the face, the anus (See Illustration 2).

[ILLUSTRATIONS 1-2 OMITTED]

A nerve, also called a neuron (or neurone) has two parts: the cell body and the axon, a long "wire" that the cell body sends out to communicate the cell body's message to other parts of the body. The axon "wire" joins other axons from similar neurons and travels from the cortex at the top of the surface of the brain through the center of the brain (or "white matter"). The axons then go down into and through the brainstem into the spinal cord, grouping together like telephone cables as they meet in their travels through the brain. They arrive at a group of cells in the spinal cord called the lower motor nerves (LMNs).

The spinal cord has layers, top to bottom, where different axon types end their journeys. The axons for the arms end in the cervical spine (at the neck); the axons for the legs in the lumbar spine (lower back) (See Illustration 3). The axons for the feet can travel three feet or more to get to the bottom of the spinal cord. Each lower motor nerve has a cell body in the spinal cord that sends its own "wire" or axon out of the spinal cord. It gets grouped together with other axons to form nerves, travels out to the muscle, connects to the muscle, and makes the muscle contract or move. Each muscle in the body has at least one LMN going to it. The finer the movement the muscle makes, the more control it needs, and so more LMNs exist to stimulate it.

[ILLUSTRATION 3 OMITTED]

The CNS controls how fast and how hard a muscle contracts. It does that by using information from sensors throughout the body. Sensors on every joint in the body tell the position of that joint. Other sensors measure temperature, limb position and how far a muscle is stretched, as well as any pain or pressure. All this information is sent to the central nervous system through nerves that go from sensors to the spinal cord, and then up the spinal cord to various areas of the brain.

Other impotent nerve tracts

A very important set of secondary motor tracts which come from other areas of the brain groups are also important for understanding cerebral palsy. One originates deep in the brain in an area called the basal ganglia and thalamus. These tracts go through the spinal cord to LMNs and influence movement in the extremities.

Another group of nerves cells are in a part of the brain called the cerebellum. The nerves in the cerebellum receive input from sensors and act through feedback loops with the LMNs to make movement smooth and coordinated. The cerebellum also coordinates the contraction of the back muscles around the spine so that it is possible for us to stand and sit up straight, as well as help us regain our balance when we trip or bend.

Moving the muscle

That brings us back to the LMNs in the spinal cord. A nerve cell is nothing more than a very tiny computer. A LMN receives input from many sources, including the upper motor neuron, the secondary motor tracts deep in the brain and cerebellum, and from sensors throughout the body (especially those from the particular area that a particular LMN supplies). Some of the input is stimulating and makes the nerve more likely to fire and send an impulse to the muscle to contract. Other inputs are inhibitory, and make the nerve less likely to fire.

A muscle can be made to contract in two basic ways. One is as a result of a command from the brain through the UMN. The second way is through a reflex.

A reflex is a very basic movement of a group of muscles in response to a stimulus. The stretch reflex is a reflex familiar to everyone. It makes the leg kick up when the doctor strikes the knee with a rubber reflex hammer. An important reflex is the withdrawal reflex. This reflex occurs in response to your hand touching something hot. Your entire arm withdraws rapidly--even before you can say "ouch."

Reflexes are able to do rapid movements because they involve only the sensory nerve going to the spinal cord with the painful signal and the LMN it reaches, going from the spinal cord back to the muscles. A strong sensory stimulus will make the LMNs for the muscles in the arm fire vigorously and contract the muscles necessary to withdraw the arm. At the same time, each LMN sends messages to and receives messages from other neurons in the spinal cord. These messages tell other LMNs to relax or contract the other muscles in the arm so that the arm can withdraw from the painful object.

The UMNs from the brain are able to completely inhibit reflex movement. Your brain, through the UMNs, can override the withdrawal reflex and have you grab a hot object and even burn yourself.

Muscle tone

The last part of the motor system to understand is the concept of muscle tone. This term does not refer to the buff look movie stars and athletes might achieve from working out regularly with weights. Rather, it is a description of how muscles work. "Tone" refers to the muscle's degree of contraction.

Muscles are always slightly contracted. Even at rest, they do not flop loosely over the bones to which they are attached. The degree of contraction is determined by the LMN. It receives input from the brain through the UMNs and sensory input from nearby pain, temperature, and muscle stretch receptors. The LMN adds together the stimulating and inhibiting messages it gets at any one time and sets the muscle tone. The LMN constantly readjusts the tone based on the amount of inhibition- and stimulation-information it gets at any one moment.

Every joint in the body has a muscle that will bend (flex) it and one that will straighten (extend) it. You can, for example, bend or straighten your arm around the elbow. When your arm bends, the bicep muscle has contracted. For the bending motion to occur, it is also essential that the tricep muscle that normally straightens the arm, relaxes and does not fight the bending motion. The bicep muscle tone is greater than the tricep muscle tone. The motor system of stimulating and inhibiting messages (described above), acts to reduce the tone in the triceps muscle when the biceps muscle contracts.

So, when you decided to scratch your nose: Your brain receives messages from sensors at the nose. It, in turn, sends a message to the UMNs in the motor cortex of your brain. These UMNs send messages along their axons through the center of the brain, brainstem, and spinal cord to the LMNs in the spinal cord. The UMN sends excitatory messages to the LMNs to tell them to contract, as well as inhibitory messages to control reflexes and muscle tone. As the final common pathway to the muscle, the LMN receives input from many areas of the brain and spinal cord. The LMN balances out their messages to: set the tone in the muscle, relax the muscle when the opposite muscle contracts, respond to stimuli with protective reflexes, and contract the muscle in response to command from the brain. The result: The itch is scratched.

Cerebral palsy and movement

Cerebral palsy affects the motor system in several ways. There can be weakness, decreased fine movement, increases or decreases in tone, or abnormal uncontrolled movement. The nose that requires scratching may never be reached, may be overshot by arm or hand, or may be hit by a hand and fingers that have not received the necessary messages about tone.

Spasticity is one of the most common characteristics of cerebral palsy, though not limited to it. Spasticity can also be a very common symptom in people with neurological injuries. The definition of spasticity most often used notes that spasticity is a motor disorder, with increased excitability of the stretch reflex, leading to a velocity-dependent increase in tone as part of the upper motor neuron syndrome. Translating that definition one part at a time:

1) "Spasticity is a motor disorder"--it involves movement.

2) "with increased excitability of the stretch reflex"--all people with spasticity have hyperactive stretch reflexes, meaning their extremities jump very briskly when the doctor hits the tendon with the hammer. The reflexes will often start by themselves leading to the repetitive jumping of the extremity when it is bent. That is called clonus.

3) "leading to a velocity-dependent increase in tone"--velocity-dependent means that the amount of increase in tone is related to how fast an extremity is moved. For people with spasticity, if the extremity is extended slowly, it can often be straightened. But if the extremity is extended rapidly, the tone kicks in and the extremity cannot be moved.

4) "as part of the upper motor neuron syndrome"--this is the site of the injury to the motor system that leads to spasticity, (i.e., in the UMN). With the damage, the UMN is unable to override reflexes and keep an extremity from moving.

The UMNs' axons or wires travel from the top of the brain in the motor cortex through the center of the brain. In the center of the brain are fluid chambers called the ventricles. The UMNs travel alongside the walls of the ventricles as they go through the brain down to the spinal cord.

Babies who are born prematurely still have a premature brain circulation. The material that insulates the developed brain--myelin--is not yet in place. This premature circulation leaves the walls of the ventricles very susceptible to damage from low blood pressure, as well as from bleeding due to high blood pressure or stress.

People who have spastic diplegia or quadriplegia will often have damage to the UMNs where they pass next to the ventricles. When children with spastic cerebral palsy have an ultrasound, CT scan, or MRI scan of the brain, they will often be reported to have PVL. The term PVL stands for periventricular leukomalacia. Translated from Latin, this means that there is damage to the white matter next to the ventricles.

The UMN axons and other motor tracts are part of the white matter of the brain. Severe hydrocephalus, which is increased fluid in the ventricles, likewise can damage a UMN as it travels next to the ventricles and lead to spasticity. Widespread injury to the brain, as is seen in infections like meningitis and encephalitis, trauma from birth or from shaken infant syndrome, lack of oxygen, or a stroke can all lead to damage to a UMN. The degree of damage, as well as the specific area of damage, will determine the areas of the body that will have spasticity. Spastic hemiplegia (weakness in half of the body) may be the result of a stroke that only involves one half of the brain.

An infant with spasticity will only show signs of increased stiffness and possibly some abnormal postures. The real problems with spasticity show up when the infant or toddler begins to make movements. The weakness that always accompanies a UMN injury reveals itself in delayed or missed developmental milestones.

Tug of war

The increase in tone leads to the classic postures of a child who has spasticity. These postures are a reflection of the widespread increases in tone. The tone is increased in all of the muscles, and therefore the strongest muscles that act on each joint will win over the others and pull the extremity toward it.

Children with lower extremity spasticity walk on their toes. Their knees and hips are bent and their legs scissor. This is because the strongest of the pair of muscles that move the leg across each of the joints of the leg has won the tug of war.

The abnormal postures that develop with the uncontrolled contraction of the muscles will lead to shortening of the tendons over time, because the tendons are never stretched out. The scissoring of the legs makes walking very difficult because the child trips over his own legs as they cross in front of him. Balance is very difficult if you have muscles that do not relax, or are weak and do not have the fine control necessary to correct a loss of balance. The increase in tone and failure to relax the muscles make every motion of a spastic limb more difficult. The movements take much more energy than normal movements, almost as if the child is trying to walk in water `all the time. Their speed of movement and the precision of their movements are impaired.

Children with severe spasticity have difficulty with every aspect of daily living. Sitting in a chair is difficult because they are either hyper flexed at the hips or have spasms that extend to their back. Dressing and hygiene can be difficult as their hip adductor muscles pull their legs together. The spasticity involving the face often makes it difficult for them to talk or eat. The clenched hands can prevent them from picking up a toy or eating utensil.

Athetoid and dystonic cerebral palsy is caused when the injury involves the deep motor neuron of the brain in the thalamus and basal ganglia. These tracts help modulate movements and when their influence on the LMN is lost through injury, the patient develops abnormal uncontrollable postures or movements.

Ataxic cerebral palsy is caused when the injury is to the neurons of the cerebellum. These neurons form the feedback loops that allow smooth coordinated movements and allow us to stand upright. Damage to those areas will lead to the difficulties with coordinated movement and standing seen in ataxic cerebral palsy. Reaching out will lead to overshooting or undershooting the object to be grasped. Walking will resemble a drunken gait.

All children who have hypotonia (decreased muscle tone) have weakness to some extent. Hypotonia can be identified immediately after an insult to the brain. Many children with spaticity were originally hypotonic. An infant with hypotonia will be floppy. Tiffs is a clinical expression doctors use because muscle tone is so inhibited that the infant lies like a rag doll.

Children with hypotonia will miss or be delayed in the achievement of normal developmental milestones. Children who have severe hypotonia will need support even to sit in a chair. They cannot support their spine or even hold their heads up straight. The weakness of theft facial muscles can make eating difficult. Children with hypotonia who can ambulate may waddle and exhibit spinal curvatures.

Hypotonia can have several causes in children. When the brain is not responsible for this motor problem, it is not classified as cerebral palsy. Examples include damage to the lower motor neuron in the spinal cord, to its axon on its way to the muscle, or in its connection with the muscle. All of these can potentially lead to decreased tone in the muscle, but not be labeled cerebral palsy. Injury or disease that prevents the normal contraction of the muscle will also cause a decrease in tone.

Children with dystonia and athetosis often have some element of spasticity. They have the same abnormal movements of their extremities at rest. An unexpected sudden movement or an extremity or of their trunks is not uncommon. This necessitates being strapped into their wheelchairs to keep them from being thrown out. Ambulation in children with significant dystonia or athetosis is difficult because of the abnormal postures and only the very mildly affected can ambulate.

Each child is special

Each child is an individual, and the impairments that a child has are as unique to him or her as a sense of humor, a competitive streak, or a special talent or interest. An individual child can have a pure spastic cerebral palsy, but ninny children have a mixture of types of cerebral palsy. The initial insult may have injured other areas of the brain and any associated intellectual impairment will significantly alter the child's function.

The ability to improve the quality of life of these children has advanced significantly in the past decade. Many interventions are available aimed at improving the function and quality of life of the child. These will be discussed next month. Even small improvements in function can make a huge difference in the quality of each individual life. Maybe even to scratch a nose.

Glossary

Axon: One of the two parts of the nerve (which is also called the neuron). The "wire" that relays messages to and from the brain and spine, and to and from the spine and muscles.

Basal ganglia: An area deep in the brain that influences voluntary movement in the arms, legs, hands, and feet.

Central nervous system: The brain and the spinal cord are the central nervous system (CNS). The CNS is responsible for thinking, learning, and speech, as well as movement.

Cerebellum: The area deep at the base of the brain that coordinates movement and balance.

Clonus: Rapid alternation between muscle contraction and relaxation caused by overactivity of the stretch reflex.

Hypotonia: Low muscle tone that interferes with the ability of the muscle to move normally.

Lower motor nerve (LMN): The nerve located in the spine that receives and messages from the brain and sensors in the body, and sends messages to the muscle to produce and control movement.

Muscle tone: The amount of contraction of a muscle when it is at rest. Muscle tone that is too high is called spasticity. High muscle tone interferes with the ability of muscle to move. Muscle tone that is too low is called hypotonia, which also interferes with movement.

Neuron: See Nerve.

Nerve: The nerve is made up of the nerve cell body and the axon. The nerve cell body receives messages from the brain and from the muscles, and processes them to provide balance and movement for the body. The axon is the "wire" by which messages are sent. Also called a neuron. Groups of axons traveling through the body are also called nerves. The major nerve in the leg, for example, is the sciatic nerve.

Nerve cell body: The nerve cell body is a tiny computer that receives input from many sources and sends messages along its axon. Also called a neuron cell body.

Reflex: A patterned response of a muscle or group of muscles in response to a stimulus.

Spasticity: A condition characterized by increased muscle tone due to damage in the upper motor neuron.

Thalamus: A group of neurons deep in the brain that influences movement and sensation throughout the body.

Upper motor nerve (UMN): Receives messages from throughout the brain and sensors in the body to control movement.

Velocity-dependent: When the ability to flex a muscle depends on the speed in which you do it. For a child with spasticity, a contracted muscle may straighten if moved slowly, but lock up if attempted to move quickly, if so, it is said to be velocity-dependent.

RESOURCE LIST FOR FAMILIES AND CAREGIVERS

For Siblings, Teens, and Younger Children

Friends in the Park, Rochelle Bennett. Checkerboard, Yardley, PA, 1992, (215) 493-8228. Price: $9.95; available through UCP Materials Center for $7.95.

Friends at School, Rochelle Bennett. Star Bright Books, New York, NY, 1995, (800) 788-4439. Price: $12.95; available through UCP Materials Center for $9.95.

I'm the Big Sister Now, Michelle Emmert. Albert & Whitman Co., Morton Grove, IL, 1989, (800) 255-7675. Price: $14.95; available from the EXCEPTIONAL PARENT Library.

Princess Pooh, Kathleen M. Muldoon. Albert & Whitman Co., PLACE, 1989. Price: $14.95; available from the EXCEPTIONAL PARENT Library.

Taking Charge: Teenagers Talk About Life & Physical Disabilities, Kay H. Kriegsman, Ph.D., Elinor L. Zaslow, M.A., and Jennifer D'Zmura-Rechsteiner, M.A. Woodbine House, Bethesda, MD, 1992. Price: $14.95; available from publisher, call (800) 843-7323; available through the UCP Materials Center for $12.95.

Walk with Me, Eric Grimm (a child with cerebral palsy). United Cerebral Palsy, Washington, DC, 1992. Price: $6.00; available through the UCP Materials Center.

UCP Materials Center UCP Materials Center, 5736 Industry Lane, Frederick, MD 21701-7226; by fax: (301) 695-1875; by E-Mail: bookshelf@UCPA.org

EXCEPTIONAL PARENT Library EXCEPTIONAL PARENT, Dept. EPCAT598, P.O. Box 1807, Englewood Cliffs, NJ 07632-1207; by phone: (800)535-1910; by E-mail: EPLIBRARY@aol.com

We Move 204 West 84th Street New York, NY 10024 telephone: (800) 437-6682 fax: (212) 987-7363 or (212) 875-8389 website: http://www.wemove.org

We Move is a not-for-profit organization dedicated to providing information, support, and educational materials to people with movement disorders, their advocates, and healthcare professionals. The group's goal is to promote awareness of movement disorders for the purpose of early diagnosis, appropriate treatment and patient support. The organization provides a comprehensive listing of national, regional and international support organizations and foundation committed to improving the quality of life for people with movement disorders. It appears on the We Move Web site and in The EXCEPTIONAL PARENT 1999 Resource Guide.

This list was developed with the staff and volunteers of United Cerebral Palsy-New York City.

Motor problems associated with cerebral palsy
Motor Problem Site of Injury

Spasticity Upper motor neuron (UMN)
Dystonia, Athetosis, Ballismus Deep motor neurons
 (basal ganglia, thalamus
Ataxia Cerebellar neurons (cerebellum)
Hypotonia Lower motor neuron (LMN)


Michael S. Turner; M.D., is a pediatric neurosurgeon in practice with the Indianapolis Neurosurgical Group and on staff of most hospitals in Indianapolis. As a pediatric neurosurgeon, his special interests include congenital neurologic disorders (.such as cerebral pals/I), brain tumors, and head injuries and trauma. He and his three teenage children live in, Indianapolis.
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Author:Turner, Michael S.
Publication:The Exceptional Parent
Date:May 1, 1999
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