In cerebral palsy, muscles are stiff or floppy, and lack control. Tendons can shorten and need stretching exercise and sometimes surgery to loosen them. Muscular changes affecting the spine can cause it to go gradually out of shape, and if not treated, this can also sometimes affect the chest and breathing. Why does damage to the brain cause this?
Normally, when you want to move, electrical impulses come from the brain, down through the spinal cord and are transmitted through the motor nerves to the muscles. This releases a chain of chemical signals starting at the junction between the nerve end and the muscle (the motor end plate), leading to contraction and shortening of the muscle. When the signal for contraction ends, calcium is pumped back and the muscle relaxes. Both of these processes take up energy and fuel, and may not be so efficient if you are tired.
What happens differently in a person with cerebral palsy, is a mechanism that is still under investigation. Currently, therefore, treatment for motor problems in cerebral palsy concentrates on the functioning – i.e. working on the muscles etc. – rather than on the underlying damage. By this means, the attempt is made to influence the brain through the plasticity (= ability to change) of the motor cortex. Plasticity is greater in a younger child. One known effect of the cortical reorganisation that has taken place in a child with cerebral palsy, is a difference in the parts of the brain that influence sides of the body (laterality) – normally it is the left side of the brain that influences the right side of the body, and vice versa, but in cerebral palsy this gets mixed up. In addition the brain signals to the muscles differently, so that contraction and relaxation are not efficient and are difficult to achieve at will. This leads to permanent tension (high tone or hypertonia), floppiness (low tone or hypotonia), or a mixture of both, with the result that muscles, with the tissues around them including the tendons and bones, may fail to develop properly and / or atrophy.
Other functions performed by the brain that may be muddled include: which muscles to contract to perform an action; how to move (for example, where to move the hand to in order to pick something up); how much force is needed to perform an action; judging size and distance (for example, how much water is in a glass); and how to operate other parts of the body that are involved in making a movement (for example, leaning forwards in order to pick something up). A child with cerebral palsy may be able to learn all these things intellectually, but still find it difficult to get the body to move in the ways they want.
One immediate effect of all this is that children with cerebral palsy tend to need periods of rest because of the extra energy they are expending in order to function.
To understand more about movement, please see Scientific Learning Corporation, “The Anatomy of Movement”, http://tinyurl.com/333jdd
