Why does the brain have two sides?
The cerebrum is divided lengthways into two halves, called cerebral hemispheres. Each side of the brain controls the opposite side of the body. For example, if you move your right leg, the instructions for that movement come from the left side of the brain. The nerve cells that carry messages from the brain cross over at the base of the brain. In most people the left side controls speaking, writing and logical thought, while the right side controls artistic abilities and creative thinking. Most people seem to use one side more than the other. This is why some people seem to be more artistic than others, or are better at scientific and mathematical thinking. Usually the left side of the brain is more dominant as far as movement is concerned, which is why most people are right-handed. About 10 percent of people are left-handed.
How does the brain allow us to make careful movements?
Fine movements are possible because the cerebellum filters instructions from other parts of the brain to the muscles. It monitors these instructions and ensures that the muscles work together. The cerebellum is part of the brain that is well understood. Its neurones are arranged in a regular pattern and it has been possible to trace the electrical circuits from one neurone to another. This part of the brain works very much like a computer.
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