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How does the Nervous System Work?

Michael Anissimov
Updated Feb 17, 2024
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The human nervous system is possibly the single most complex object in the entire cosmos, or at least the most complex object in our section of the galaxy. This is because it includes the brain, with ten billion neurons and many times more interneural connections. The human brain is a more dense source of complexity than anything we have yet seen, including the bodies of all animals and any variety of inanimate phenomena or objects.

However, it is more than just the brain. All animals have a nervous system, but only vertebrates have a complex nervous system that include the central nervous system (CNS) and peripheral nervous system (PNS) as components. The CNS consists of the nerves and neurons found in the spine and brain, while the PNS is everything else.

In older animals, the nervous system was mainly a sensor network connected directly to the skeletomuscular system, allowing external and internal causes to give rise to organism-centric effects called behaviors. In more complex organisms, it functions as an independent entity, processing inputs extensively before returning carefully chosen outputs. In all animals, including humans, the vast majority of this is unconscious, automatically executed by neural programs that have been hardwired by millions of years of evolutionary design.

The central nervous system is the most complex system and the most difficult to understand or reverse-engineer in any species, although efforts in this direction have had some success. For the purposes of this article, it can be thought of as the brain and spine, which includes the brain stem. Further subdivisions are the province of cognitive science and neuroanatomy.

The peripheral nervous system has several subdivisions. The first level consists of the somatic nervous system and the autonomic nervous system, which refer to the nerves just under the skin and the nerves everywhere else, respectively. Despite their names, both mostly execute automatically, but the autonomic system is so named because it is responsible for the body’s maintenance functions, which have a reputation for being opaque to conscious control. The nerves we use to consciously control our bodies are part of the somatic system, but these function automatically even in the event of a coma.

The autonomic nervous system is further divided into sympathetic and parasympathetic. A third division, the enteric nervous system, is also occasionally referred to. The sympathetic system responds to stress, danger, and the like, and is responsible for the release of adrenaline, among other things. The parasympathetic system is dominant during rest and helps us go to sleep and digest food. These two tend to balance each other, creating a degree of harmony in the body. The enteric system is responsible for some nerves around the intestines, and is known to function properly even when disconnected from the other two systems.

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Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated WiseGeek contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By anon334193 — On May 10, 2013

I don't comprehend how this can be intricate for some of you. This is actually basic information.

By anon270156 — On May 21, 2012

I agree the nervous system is the most complex thing.

By anon223344 — On Oct 18, 2011

This indeed helped me do my research. We have to do a project in my health class and this felt like the right one, though it is a difficult system.

By anon183979 — On Jun 07, 2011

It helps me with my assignment I'm doing right now, Therefore, it's a little bit hard to understand this lesson (for me) because there's so many parts of it and i only want key words but they're hard to understand. Just thinking about it right now, right here in front of the computer. But at least, this article did help me with my assignment. Thanks a lot!

By KingDream — On Jul 14, 2010

@ehernandez, It is always best to resort to the easiest, and most elementary level explanations to learn the basics before moving on to something more in depth. If you consult a children's book, then revert back to the article, it might help you understand it a bit better. Good luck!

By ehernandez — On Aug 26, 2009

I like to call it, 'Super Human Highway', very complicated indeed. Good article, but I'm looking for some easy read material that explains and breaks down each category of the nervous system, any suggestions? Something for the 'laymen'. I think my sympathetic nervous system is going into overdrive trying to understand all this. Thanks.

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated WiseGeek contributor and brings his expertise in paleontology, physics, biology,...
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