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I'm interested in the Sympathetic Nervous System. How does it work? What nerves make the different organs in the human body work? What happens when something goes wrong? Can this system be fixed?
Question Date: 1999-02-08
Answer 1:

Before we talk about the sympathetic nervous system, let's talk about the autonomic nervous system (which the sympathetic nervous system is a part of).

The autonomic nervous system is sort of a headquarters for running our body. Its name comes from "autonomous", and it runs your bodily functions without your awareness or control. It is divided into two systems which, where they act together, often oppose each other: the sympathetic and parasympathetic systems. The sympathetic system causes you to get ready to act quickly. In other words, if you're about to get hit by a car (remember, don't play in the street!), your sympathetic nervous system will react to prepare you to escape that situation. For example your pupils in your eyes dilate, muscle vasculature dilates (this makes more blood flow to your muscles), your heart rate increases, and your digestive system is put on hold. That's what the sympathetic nervous system does.

The parasympathetic system has some opposite functions, including slowing the heart, constricting the pupils, stimulating the gut and salivary glands, and other responses that are not a priority when being "chased by a car". The state of the body at any given time represents a balance between these two systems.

When something goes wrong, it usually causes your body to be unable to trigger these responses. As such, people with diseased autonomic nervous systems may hold their hand over a fire and react too slowly to keep themselves from getting burned, or they step on something sharp but react slower than others. I'm not sure what can be done about that, but doctors are getting better at treating neurological diseases. New medicines have been created recently which help out a lot. However, I don't know the exact details about what the medicines do. I hope this helps you out! Thanks for writing...

Answer 2:

Well, the sympathetic nervous system controls the "fight or flight" response. It is like the body's alarm system.When something scares you or makes you really mad, this system kicks in. You are familiar with the feeling: your heart beats fast, you breathe harder and your stomach feels weird. All of these responses have to do with getting blood (and the oxygen and sugar it carries) to places like your brain, heart and muscles. Your stomach feels odd because blood is going away from your gut to supply the other areas. You sweat in order to cool your body as you fight or run, and your vision "narrows" to allow you to see far away objects better.

Fight or flight is an evolutionary leftover. In our modern lives, we can't make most scary situations better by running or fighting. In fact one of the fight or flight responses, hair standing on end, is pretty useless now (but it makes a cat look bigger). Some parts of this response are actually damaging to the body. For example, your sensitivity to pain is reduced, so you're more likely to stay in the soccer game with a hurt knee, making it worse.

Two things make the sympathetic nervous system work: nerves and the hormone adrenaline (epinephrine). The nerves work faster, but adrenaline lasts 10 times longer. What is a hormone? Where is adrenaline made?

Thanks for asking,

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