The parasympathetic nervous system is one of two divisions of the autonomic nervous system (ANS), the other being the sympathetic nervous system. The ANS controls the body's automatic or unconscious functions, such as heart rate, digestion, and breathing.
The activity of the parasympathetic nervous system can be summarized as ‘rest and digest’ because it slows the heart rate and keeps the body's energy use as low as possible to stimulate organs like the gastrointestinal tract and the bladder.
In the parasympathetic nervous system, preganglionic cholinergic neurons release acetylcholine to activate postganglionic cholinergic neurons, which then release acetylcholine to target cells. Thus, their nerve fibers are referred to as cholinergic fibers.
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