The majority (approximately 98%) of neural tissue is found within the brain and the spinal cord. It is composed of two basic classes of cells: nerve cells (or neurons), which transmit communication signals, and glial cells, which act to support both the structure and function of neurons (Carlson, 2004).The parenchyma of the brain is nervous tissue (nerve cells and glia). The blood vessels within the brain and the connective tissue associated with these blood vessels are stroma. The parenchyma of the malignant neoplasm is cancer cells.