The central nervous system (CNS) is the processing center for the nervous system. It receives information from and sends information to the peripheral nervous system. The two main organs of the CNS are the brain and spinal cord.he brain processes and interprets sensory information sent from the spinal cord. Both the brain and spinal cord are protected by three layers of connective tissue called the meninges. Within the central nervous system is a system of hollow cavities called ventricles.
The edge of something is the end of it, the outer limit. You can sit on the edge of your desk, on the edge of a chair, on the edge of a cliff. As stated by someone else, sitting on the edge of your seat is used to indicate tension or anticipation. You are ready to jump up out of the seat as quickly as possible.
An edge is a line segment. It connects vertices together. In a two-dimensional object like the hexagon above, we sometimes call it a side. A flat surface (like the hexagon itself, or any of the flat sides of the 3-D figure on the right) is usually called a face, but sometimes we call it a side too. That's why we usually try to avoid the word side when working with 3-D objects because it is less clear than using the terms edge and face instead.