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 body.

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 cortex).

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 rupture, the 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 be paralyzed?

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 shown below:

cheese, ice cream, whole milk, and other dairy products "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.