Introduction Brain tumors are not rare. About 20,000 Americans are diagnosed with brain cancer or related cancer of the nervous system. This reference summary will help you understand how brain tumors are diagnosed and what options are available to treat them. The Brain The brain is the most important organ in the body. It controls the 5 senses, as well as the ability to speak and move. Brain Skull The right side of the brain controls the left side of the body. The left side of the brain controls the right side of the body. The brain is protected by the skull and is covered by a special covering known as “dura.” There are many different types of cells in the brain. The thinking cells, the cells responsible for brain activity, are known as “neurons.” The other cells in the brain help take care of the neurons; they are known as “glial cells.” Cancer And Its Causes The body is made up of very small cells. Normal cells in the body grow and die in a controlled way.