The Brain Helps Us Move
Did you know that your body is mapped in the
brain? On the outer surface of the brain, called the cortex, the
cells send nerves to specific muscles. Therefore, when you tell your
brain that you want to move your arm to scratch your face, the brain has
a map of the muscles of the arm and it "knows" which muscles to
make contract. The motor-control cells operate muscles on the opposite side of
| The surface
("cortex") of the human brain that contains the
motor map is outlined in white. Cells here issue commands to move
certain body parts. A similar sensation map of the
body (the second circled area, lies just behind the motor
These maps have been constructed by brain
surgeons who applied mild electrical current to different parts
of the cortex and observed which muscles contracted.
Coordination of motor commands is accomplished
by the cerebellum, which lies just above the spinal cord at the
back of the brain. There are also major motor control systems
located underneath the cortex.
Common Diseases of Motor System
Stroke. If an artery on the surface of the brain gets plugged
up or if the vessels
blood supply to the motor cortex would be cut off. This is a common
symptom of the condition called "stroke." The lack of
blood supply kills neurons in the affected parts of the motor map. The fibers
coming from the motor map cross over in the brainstem to the other side.
So, if a stroke occurred on the right side of the body, which side would
The environment can affect the likelihood of stroke
in the sense that clogging of arteries is often caused by eating too
much of the kinds of food that raise the blood level of fats and
cholesterol. Do you know what foods do that? A partial list is
- cheese, ice cream, whole milk, and other dairy
- "french fried" anything
- greasy hamburgers and fatty meat of any kind
Parkinson's Disease. Have you known or seen
someone with Parkinson's disease? In this disease, the limbs tremble and
shake uncontrollably. The cause is not a damaged motor map, but rather
damage to one of the motor systems located beneath the cortex.
This area, called the caudate nucleus, normally prevents trembling. But
in Parkinson's disease, the cells in the caudate do not get enough
stimulation by dopamine, a neurotransmitter that is supplied by cells in
a particular part of the brainstem.
Environmental toxins may cause this disease, although
the research is not yet conclusive.
|Pfizer Inc. has a very interesting Web site on the brain. To
play one of the more interesting games, click
here. Take the "tour" at this site.