Central Nervous System
The Central Nervous System (CNS) is a very complex, highly organized structure. It consists of the brain in the skull and the spinal cord, which threads through holes down the middle of the vertebrae (bones that make up the vertebral column ["backbone"]). The front half (roughly) of the CNS organizes and controls movement; the back half receives and processes information from the senses. The CNS is organized as a hierarchy (organized in graded layers, higher layers controlling lower layers as in the military [general > colonel > major > lieutenant]). Each level from the cerebral hemispheres at the top controls the levels below it. Unlike most hierarchies, the higher the level the more parts to it, at least in the brains of mammals, especially humans. The hierarchy has three main levels, cerebral hemispheres > brain stem > spinal cord.