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This question originally appeared on Quora. Answer by Fabian van den Berg, neuropsychologist.

It is composed of neurons to send and receive signals, and supported by an array of cells to maintain these neurons and provide the necessary nutrition. So what is in the nervous system? Let’s have a look.

First off we have the Central Nervous system, which is your Brain and your Spinal Cord, this is the central command of your body. It delegates and coordinates all the inputs and outputs to make the meat-bag move like a puppet.

The Peripheral Nervous System is the connection between the body and the Central Nervous System. These are all the nerves and ganglia outside of the brain and spinal cord. Unlike the central nervous system the PNS is a bit more exposed. It’s not encased in bone nor protected by a blood-brain-barrier. The Peripheral Nervous System is divided into two parts: the Somatic and Autonomic Nervous System.

The Somatic Nervous System is what makes you move, it governs the conscious control you need to walk, look around, or type. It also relays the information you get from touch. Afferent connections are sensory connections, these go towards the Central Nervous System. Efferent Connections are motor connections, these go towards the muscles.

The Autonomic Nervous System is…well everything else. It controls everything that happens whether you want it or not. It controls all the organs like the heart. This system can also be divided into three parts: Sympathetic, Parasympathetic and nowadays also the Enteric Nervous System.

  • The Sympathetic Nervous System is the one that amps you up, it initiates the Fight or Flight mechanism and keeps everything balanced. It works in tandem with the Parasympathetic Nervous System which does the opposite.
  • The Parasympathetic Nervous system calms you down and controls anything you can do when not running for your life. Things like sexual arousal, tear production, urination, defecation, etc. Together with the Sympathetic Nervous system it keeps the balance.
  • The Enteric Nervous System is a fairly new division that is separate from the Autonomic Nervous System. I still put it under it because it communicates to the CNS via the Autonomic Nervous System. This is basically your second brain, your gut brain. It operates independently to digest food. It communicates a lot with the rest of the nervous system, but it is able to function without being connected. It has its own reflexes and can alter its behavior based on the food going through. It even has its own support cells and a barrier similar to the Blood-Brain-Barrier. So it’s quite special in its structure and ability to influence the brain.

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