The Parasympathetic Nervous System

The parasympathetic nervous system restores the body during calm times when there are no threats, and is often called the rest and digest system.

It is one of the major divisions of the autonomic nervous system, which controls involuntary functions by regulating the activity of smooth muscle in visceral organs, cardiac muscle in the heart, and certain glands, such as the salivary glands.

When the parasympathetic nervous system is activated, signals from preganglionic neurons in the brain stem, and sacral part of the spinal cord are sent to ganglia, clusters of neuronal cell bodies in the peripheral nervous system, near the organs or glands being controlled.

Here, the message is transmitted to postganglionic neurons, which typically use the neurotransmitter acetylcholine to regulate activity of target tissues. For example, they lower heart rate, relaxing the body, and stimulate muscle contraction in the intestines and bladder, promoting digestion and excretion.

As a result, the parasympathetic system helps rebuild energy stores and maintain homeostasis at times when the body is able to rest.