Flexi Says: The nervous system is a complex network of nervous tissue that carries electrical messages throughout the body. It includes the brain and spinal cord, the central nervous system, and nerves that run throughout the body, the peripheral nervous system. Although the nervous system is very complex, nervous tissue consists of just two basic types of nerve cells: neurons and glial cells. Neurons are the structural and functional units of the nervous system. They transmit electrical signals, called nerve impulses. Glial cells provide support for neurons. For example, they provide neurons with nutrients and other materials.