Parasympathetic Nervous System: Definition, Function & Effects

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  • 0:02 Introduction
  • 0:37 The Autonomic Nervous System
  • 2:04 The Parasympathetic…
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: John Williams
The autonomic nervous system is responsible for controlling bodily processes that are not under our own voluntary control. Under normal circumstances, the parasympathetic division of the ANS is the most active. This article discusses the function of the parasympathetic nervous system in the human body.

Day-to-Day Activities

Imagine it's a typical day of your life, and you're sitting down to eat one of your daily meals. You eat the meal, your body begins to digest it, and you move on to the next task at hand. Doesn't sound really exciting, does it?

As it turns out, in the course of our normal daily activities, the nervous system is actively working to ensure that you are able to function in this normal, day-to-day existence. Specifically, it is the parasympathetic nervous system that controls the body processes under normal circumstances.

The Autonomic Nervous System

The autonomic nervous system, or ANS, is the portion of the nervous system that regulates involuntary processes. In other words, these are processes that are not under conscious control. The ANS is divided into two divisions: the parasympathetic and the sympathetic nervous systems.

The sympathetic nervous system, also called 'fight-or-flight' activation, is the segment that prepares the body for emergency situations. Since emergency situations are typically not common, most people are infrequently under sympathetic nervous activation.

The parasympathetic nervous system, also known as the 'rest and digest' activation, is the segment that assists with normal, autonomic functions. In other words, you are typically in parasympathetic nervous system control most of the time. Since this is the normal state of the body, the parasympathetic system is more active than the sympathetic system in controlling bodily functions.

Neurons in the parasympathetic nervous system utilize acetylcholine, a neurotransmitter for cell-to-cell communication. Any tissues that are controlled by the parasympathetic system will have receptors for acetylcholine so that this system can communicate with them. This communication results in several physiological processes, such as the following.

The Parasympathetic Nervous System

As the nickname 'rest and digest' implies, the parasympathetic system will be responsible for bringing the body to a restful, low activity state. Therefore, any organs, tissues, and processes that are found during these low activity states will also be controlled by this portion of the ANS. For example, the vagus nerve, also known as the 'pneumogastric' nerve, helps to modulate the rate by which the heart beats. Under parasympathetic activation, the vagus nerve will slow the heart rate down. Also, airways within the lungs constrict, or get smaller, under parasympathetic activation in order to reduce airflow and to avoid hyperventilation, which is excessive oxygen intake.

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