Your autonomic system is the branch of your peripheral nervous system that regulates the functions of your internal organs, like your heart and stomach, and also controls your smooth and cardiac muscles, and your glands.
Its effects on your organs and muscles and glands are by no means consisent.
Your autonomic system is constantly making involuntary, fine-tuned adfustments to your body, based on what signals your central nervous system is picking up.
This could mean changing your body temperature, sending extra blood to a particular area, slowing your heart beat, or tweaking your stomach secretions.
<Sympathetic & Parasympathetic Nervous Systems>
Two divisions that serve the same organs, but they create opposite effects in them, battling it out back and forth, to either excite your body's functions or subdue them.
One of them is dedicated to amping you up and preparing you for activity - that's your sympathetic nervous system.
And the other one talks you down and effectively undoes what its foil did.
That is the parasympathetic nervous system.
<Origins>
Originate at differnt sites in your body.
Your sympathetic fibers are thoracolumbar - meaning that they originate from between your thoracic vertebrae where your ribs attach, and the lumbar vertebrae just inferior to your ribs.
The nerve fibers of your parasympathetic system befin both above and below where the sympathetic ones do.
They're craniosacral, meaning they sprout from the base of your brain and also from your sacral spinal cord, just superior to the tailbone.
<Ganglia>
Both parts of your autonomic system require two neurons in order to work.
Those two neurons meet in ganglia - clusters of neuron cell bodies that house millions of synapses.
Sympathetic ganglia are found closer to the spinal cord, because in those fight-or-flight moments of high excitement or activity, they need to be able to send a single message far and wide, like the Bat Signal.
Most parasympathetic ganglia are found way out from the spine - near, or even inside of their effector organs.
<Axon Lengths>
Their neurons themseleves have slightly different forms, namely the length of their axons.
The axon lengths of the neurons before the ganglion are called the preganglionic fibers, and the ones coming out are postganglionic.
The key here is that, in the sympathetic system, the preganglionic fibers are much shorter than the post ganglionic ones.
The structure of each of these systems is related to its function.
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