The parasympathetic nervous system is a subdivision of the autonomic nervous system. It consists of nerve fibers, which originate in the brain stem. It returns the body to homeostasis. The parasympathetic nervous system promotes slowing of the heart rate, flowing of gastric juices and muscular activity of the alimentary tract.
In Our Own Words
A part of our nervous system is devoted to automatic things like breathing, sweating, and sleeping. These activities can happen without us thinking about them, and this part of our nervous system is called the autonomic nervous system. Within the autonomic nervous system, there are two opposing sub-systems that work together: sympathetic and parasympathetic.
The parasympathetic nervous system produces effects that often oppose the sympathetic nervous system—that is, calming effects that are the opposite of “fight or flight.” It promotes activities such as digestion and sleep. The parasympathetic nervous system aids with digestion, plays a role in stomach and intestinal contractions, slows the heart rate and breathing during sleep, and is responsible for many other automatic or involuntary functions and responses.