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Autonomic Nervous System: Function, Definition & Divisions

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  • 0:00 Definition: Autonomic…
  • 1:20 Sympathetic Nervous System
  • 1:50 Parasympathetic Nervous System
  • 2:20 Enteric Nervous System
  • 2:55 Lesson Summary
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Lesson Transcript
Instructor: Kimberly Carpenter

Kimberly has an undergraduate degree in Lab Sciences and a Master's degree in Education.

In this lesson we'll learn the definition of 'autonomic nervous system.' The lesson explores the system's function and gives an overview of the divisions that comprise the system. A short quiz will follow.

Definition of Autonomic Nervous System

Have you ever come face to face with something that scared the living daylights out of you? Well, if you have, then you probably know your body's immediate reaction. Your heart rate will increase and your heart will pound 'out of your chest.' Your senses, such as sight, hearing, and sometimes even smell, will be put on full alert. Your body will automatically decide whether you need to leave the situation immediately or if it is time to stay and defend yourself against whatever threat you have encountered.

These responses are all part of the autonomic nervous system (ANS) and have been put in place by the body to keep us all from danger whenever possible. Your autonomic nervous system is important for several reasons.

It keeps your cardiac muscles and smooth muscles regulated (like the ones in your stomach). It also regulates various aspects of your body's glands depending on the type of environment and conditions. It is responsible for the fight or flight response you automatically have when faced with a frightening or dangerous situation.

The autonomic nervous system is almost always involuntary, so you will have a difficult time trying to control its responses when they are triggered.

There are three divisions of the ANS: sympathetic nervous system, parasympathetic nervous system, and enteric nervous system. Each works a bit differently, but they are all vital to ensuring your body remains intact and safe.

Sympathetic Nervous System

The sympathetic nervous system is the part responsible for your fight or flight reaction, like the reaction you would have if you encountered a large animal while walking in the forest. It actually uses your body's energy to increase blood pressure, increase your heart rate, and decrease the digestive process, so you automatically go on full alert and can make the correct decision whether to leave the situation or remain face to face with the danger.

The sympathetic nervous system uses norepinephrine as a neurotransmitter to put your body on full alert.

Once the danger is over, however, the body will return to normal and your heart rate, blood pressure, and digestive system will begin working as they should.

Parasympathetic Nervous System

The second part of the ANS is the parasympathetic nervous system, which allows you to rest and digest. It is triggered when you are relaxing during a sunset or lying on the beach listening to the waves of the ocean. The key to this part of the ANS is to conserve your energy. Therefore, your blood pressure will often decrease, your pulse will become slower as you relax, and the digestive process will increase because the smooth muscles inside your body begin to work properly.

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