Neuroscience For Kids
Autonomic Nervous System
The autonomic nervous system (ANS) regulates the
functions of our internal organs (the viscera) such as the heart,
stomach and intestines. The ANS is part of the peripheral nervous system
and it also controls some of the muscles within the body. We are often
unaware of the ANS because it functions involuntary and reflexively. For
example, we do not notice when blood vessels change size or when our heart
beats faster. However, some people can be trained to control some
functions of the ANS such as heart rate or blood pressure.
The ANS is most important in two situations:
- In emergencies that cause stress and require us to "fight" or take "flight" (run away)
- In nonemergencies that allow us to "rest" and "digest."
The ANS regulates:
- Muscles
-- in the skin (around hair follicles; smooth muscle
-- around blood vessels (smooth muscle)
-- in the eye (the iris; smooth muscle)
-- in the stomach, intestines and bladder (smooth muscle)
-- of the heart (cardiac muscle)
- Glands
The ANS is divided into three parts:
- The sympathetic nervous system
- The parasympathetic nervous system
- The enteric nervous system
| The Sympathetic Nervous System | |
 | It is a nice, sunny day...you are taking a nice walk in
the park. Notice in the picture on the left that the sympathetic nervous system originates in the spinal cord. Specifically, the cell bodies of the first neuron (the preganglionic neuron) are located in the thoracic and lumbar spinal cord. Axons from these neurons project to a chain of ganglia located near the spinal cord. In most cases, this neuron makes a synapse with another neuron (post-ganglionic neuron) in the ganglion. A few preganglionic neurons go to other ganglia outside of the sympathetic chain and synapse there. The post-ganglionic neuron then projects to the "target" - either a muscle or a gland. Two more facts about the sympathetic nervous system: the synapse in the sympathetic ganglion uses acetylcholine as a neurotransmitter; the synapse of the post-ganglionic neuron with the target organ uses the neurotransmitter called norepinephrine. (Of course, there is one exception: the sympathetic post-ganglionic neuron that terminates on the sweat glands uses acetylcholine.) |
Suddenly, an
angry bear appears in your path. Do you stay and fight OR do you turn
and run away? These are "Fight or Flight" responses. In these types of
situations, your sympathetic nervous system is called into action - it
uses energy - blood pressure increases, heart beats faster, and
digestion slows.| The Parasympathetic Nervous System | |
 |
It is a nice, sunny day...you are taking a nice walk in the park.
Notice in the picture on the left, that the cell bodies of the parasympathetic nervous system are located in the spinal cord (sacral region) and in the medulla. In the medulla, the cranial nerves III, VII, IX and X form the preganglionic parasympathetic fibers. The preganglionic fiber from the medulla or spinal cord projects to ganglia very close to the target organ and makes a synapse. This synapse uses the neurotransmitter called acetylcholine. From this ganglion, the post-ganglionic neuron projects to the target organ and uses acetylcholine again at its terminal. |
This time, however, you decide to relax in comfortable chair that you have
brought along. This calls for "Rest and Digest" responses. Now is the
time for the parasympathetic nervous to work to save energy. This is when
blood pressure can decrease, pulse rate can slow, and digestion can
start.
Autonomic Nervous System
| Structure | Sympathetic Stimulation | Parasympathetic Stimulation |
|---|---|---|
| Iris (eye muscle) | Pupil dilation | Pupil constriction |
| Salivary Glands | Saliva production reduced | Saliva production increased |
| Oral/Nasal Mucosa | Mucus production reduced | Mucus production increased |
| Heart | Heart rate and force increased | Heart rate and force decreased |
| Lung | Bronchial muscle relaxed | Bronchial muscle contracted |
| Stomach | Peristalsis reduced | Gastric juice secreted; motility increased |
| Small Intestine | Motility reduced | Digestion increased |
| Large Intestine | Motility reduced | Secretions and motility increased |
| Liver | Increased conversion
of glycogen to glucose | |
| Kidney | Decreased urine secretion | Increased urine secretion |
| Adrenal medulla | Norepinephrine and epinephrine secreted | |
| Bladder | Wall relaxed Sphincter closed | Wall contracted Sphincter relaxed |
It should be noted that the autonomic nervous system is always working. It is NOT only active during "fight or flight" or "rest and digest" situations. Rather, the autonomic nervous system acts to maintain normal internal functions and works with the somatic nervous system.
The enteric nervous system is a third division of the autonomic nervous system that you do not hear much about. The enteric nervous system is a meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, and gall bladder).
 |
TRY IT! --> Interactive Word Search Puzzle about the autonomic nervous system. |
Copyright © 1996-2020, Eric H. Chudler, University of Washington
