The sympathetic and the parasympathetic nervous system are parts of what is commonly called the autonomic nervous system. (Autonomic = can not be controlled by the mind). You can say that these systems work in balance with each other and directly or indirectly affect almost every structure in the body (e.g. heartfrequence, heartcapacity, lumbar function, kidneys, blood vessels, stomach and intestines)

The sympathetic nervous system has an active "pushing" function, the parasympathetic has mainly a relaxing function.

The sympathetic nervous system is located to the sympathetic chain, which connects to skin, blood vessels and organs in the body cavity. The sympathetic chain is located on both sides of the spine and consists of ganglias.

The autonomic nervous system is most important in two situations: emergency situations that cause stress and require us to "fight" or take "flight", and nonemergency situations that allow us to "rest" and "digest". The autonomic nervous system also acts in "normal" situations to maintain normal internal functions and works with the somatic nervous system. When the body reacts to signals about e.g. danger it is the sympathetic ganglia that makes

The lungs and the bronchial tubes are widend to give us more oxygen.
The motility in the intestine is reduced - we shall not digest food - we must fight or run away!
Blood is sent to the brain while skin and internal organs get less.
Muscel tension is increased.
Heart rate and force is increased.

Below you can find a summary of some of these effects:

Sympathetic Structure Parasympathetic
Rate increased Heart Rate decreased
Force increased Heart Force decreased
Broncial muscle relaxed Lungs Broncial muscle contracted
Pupil dilation Eye Pupil constriction
Motility reduced Intestine Digestion increased
Sphincter closed Bladder Sphincter relaxed
Decreased urin secretion Kidneys Increased urin secretion

(When you read about what a complicated system the sympathetic chain is, you wonder how anyone can allow surgeons to perform ETS..)

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