central nervous system

The central nervous system, or CNS, is the brain plus the spinal cord. It is the part of the nervous system where the body gathers up everything it has sensed, makes sense of it, and decides what to do next. Signals from your skin, eyes, ears, and inner organs all flow inward to the CNS, and the commands that move your muscles and steer your organs flow back out from it. In short, it is the place where information is brought together and turned into action.

A handy picture is an airport control tower. Planes (the messages from your body) arrive from every direction; the tower takes them all in, weighs them against one another, and sends out clear instructions so nothing collides and everything keeps moving. The CNS does the same kind of work, blending many incoming streams of information into single, coordinated responses, which is why it is often called the body's integration and processing hub. The spinal cord handles the faster, more local jobs and acts as the main cable to and from the brain, while the brain handles the deeper thinking, memory, feeling, and planning.

Because so much depends on it, the CNS is the most heavily guarded tissue you have: it sits inside the bony skull and spine, is wrapped in tough membranes called the meninges, and floats in a cushion of cerebrospinal fluid. It is paired with the peripheral nervous system, the network of nerves outside the brain and cord that carries messages between the CNS and the rest of the body. Most CNS neurons in mammals do not regrow well once damaged, which is part of why brain and spinal cord injuries can leave lasting effects.