Because the brain and spinal cord affect nearly every function within the body, tumors within the brain can have major complications. Secondary brain tumors, or tumors originating from cancer in another part of the body, are much more common than primary brain tumors that begin in the brain. Brain tumors are especially complex to understand because of the many types and characteristics; however, Gliomas and Non-glioma tumors are considered the main groups, each with subgroups of its own. Glioma tumors grow from supportive cells in the brain called glial cells with astrocytes, oligodendrocytes, and ependymal cells serving as examples. Gliomas are assigned a grade to describe the aggressiveness of the tumor, with I being the slowest growing and IV being the most hostile form. Non-gliomas tumors, as the name suggests, arise from non-glial cells, of which there are many.