Parasympathetic nervous system is one of the two main divisions of the autonomic nervous system. It is responsible specifically for stimulation of activities that occur when the body is at rest. The main goal of this system is to conserve the resources of the body so that they can last longer. The parasympathetic nervous system is also known as craniosacral outflow because it arises from the brain (mixed with III, VII, IX and X cranial nerves) and sacral 2-4 segments of the spinal cord. Thus it has a cranial and a sacral part.
The preganglionic fibers are very long, reaching right up to the viscera of supply. The ganglia, called terminal ganglia, are situated mostly on the viscera and, therefore, the postganglionic fibers are very short. Parasympathetic nerve endings are cholinergic in nature, similar to the somatic nerves.
Functionally, parasympathetic activity is seen when the subject is fully relaxed. His pupils are constricted, lenses accommodated, face flushed, mouth moist, pulse slow, blood pressure low, bladder and gut contracting, and the perineal sphincters relaxed.
In general the effects of parasympathetic activity are usually discrete and isolated, and directed towards conservation and restoration of the resources of energy in the body.