Nervous system

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Illustration of how pain travels to the brain, from René Descartes's Treatise of Man

The nervous system is a system in the body which sends signals around the body. It lets people and animals respond to what is around them. The central nervous system is the brain, the spinal cord, and nerves. It is present in most animals. It is there to coordinate movement, to process the input of the senses, and to make the animals act a certain way. It is made up of neurons and cells called glia among other things. Glia cells keep the neurons safe and healthy.

The structure of the system includes the brain and spinal cord, which together are called the central nervous system. The brain has billions of nerve cells to help think, walk, and breathe. The nervous system can react in 1/100 seconds to stimulus. The stimulus is the messenger that sends letters to the part of your body that is experiencing or has experienced danger or surprise. It also sends these signals to your brain, for help to think of other ideas to protect and/or absorb the danger and/or surprise in that area of the body.

The anatomy of nervous systems can be sub-divided as follows: