Parasympathetic Nervous System

The parasympathetic nervous system is an autonomic nervous system responsible for calming the body down after stressful situations, such as fight-or-flight responses. It is part of the motor division of the peripheral nervous system, which consists of long nerves hooked up to various muscles, glands, and organs. Its main role is to stimulate and maintain the body’s normal functions during rest, stress-free activities, or non-threatening, environmental events. It is in charge of the body’s “rest and digest” functions, the opposite of the sympathetic nervous system’s “fight or flight” response. The parasympathetic system is made of three cranial nerves and two sacral autonomic nerve chains. It is responsible for regulating heart rate, controlling breathing, digestion, and urination; aiding the visual processes; controlling salivation, tear production, and sexual activities; and promoting relaxation and calming the body. Generally, it maintains homeostasis in the body. All of these processes are controlled through the vagus nerve, which is the main nerve of the parasympathetic system and connects directly to the brain stem. The two components of the parasympathetic system are the presynaptic component, which releases neurotransmitters such as acetylcholine; and the postsynaptic component, which responds to these neurotransmitters by altering membrane potentials, resulting in physiological processes. Acetylcholine is a neurotransmitter that binds to type A-nicotinic receptors on the postsynaptic cell. These receptors then open up activation channels, creating an increased permeability to potassium and calcium ions, which in turn leads to a slower heart rate, relaxation of the bronchial muscles, and constriction of the blood vessels leading to better blood circulation. In essence, the parasympathetic nervous system prepares the body for rest and relaxation. It gets the body ready for a time of reflection and relaxation by slowing the heart rate, dilating the pupil, stimulating salivation, and activating digestion. This is why it is important to spend time away from stressful situations – so the parasympathetic nervous system can kick in and restore balance to the body.