The Parasympathetic (PNS) vs Sympathetic Nervous System
The parasympathetic nervous system is one of three divisions of the autonomic nervous system. Sometimes called the rest and digest system, the parasympathetic system conserves energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract.
From Wikipedia, the free encyclopedia
The parasympathetic nervous system (abbreviated PN to avoid confusion with the peripheral nervous system (PNS)) is one of the two divisions of the autonomic nervous system, the other being the sympathetic nervous system.[1] The autonomic nervous system is responsible for regulating the body’s unconscious actions. The parasympathetic system is responsible for stimulation of “rest-and-digest” or “feed and breed”[2] activities that occur when the body is at rest, especially after eating, including sexual arousal, salivation, lacrimation (tears), urination, digestion and defecation. Its action is described as being complementary to that of the sympathetic nervous system, which is responsible for stimulating activities associated with the fight-or-flight response.
Nerve fibres of the parasympathetic nervous system arise from the central nervous system. Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve. Three spinal nerves in the sacrum (S2-4) also act as parasympathetic nerves. These are commonly referred to as the pelvic splanchnic nerves.
Because of its location, the parasympathetic system is commonly referred to as having “craniosacral outflow”, which stands in contrast to the sympathetic nervous system, which is said to have “thoracolumbar outflow”.
The sympathetic nervous system is one of the two main divisions of the autonomic nervous system, the other being the parasympathetic nervous system.[1][2] The autonomic nervous system functions to regulate the body’s unconscious actions. The sympathetic nervous system’s primary process is to stimulate the body’s fight-or-flight response. It is, however, constantly active at a basic level to maintain homeostasis.[3] The sympathetic nervous system is described as being complementary to the parasympathetic nervous system which stimulates the body to “rest-and-digest” or “feed and breed”.
The name of this system can be traced to the concept of sympathy, in the sense of “connection between parts”, first used medically by Galen.[4] In the 18th century, Winslow applied the term specifically to nerves.[5]
The main nerves of the parasympathetic system is the tenth cranial nerve, the vagus nerve. It originate in the medulla oblongata. Other preganglionic parasympathetic neurons also extend from the brain as well as from the lower tip of the spinal cord.
These are all great links for the Parasympathetic (PNS) vs Sympathetic Nervous System:
http://www.medicinenet.com/script/main/art.asp?articlekey=5607
https://faculty.washington.edu/chudler/auto.html
http://www.health.harvard.edu/staying-healthy/understanding-the-stress-response
http://www.scholarpedia.org/article/Parasympathetic

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