Parasympathetic Nervous System

Let's go through the parasympathetic nervous system definition. The parasympathetic nervous system is primarily made up of the cranial and sacral spinal nerves. Preganglionic neurons from the brain or sacral spinal cord synapse with only a few postganglionic neurons located in or near the effector organ (muscle or gland). When the body is relaxed, resting, or feeding, the parasympathetic nervous system is in charge of rest and digestion. After a stressful situation, it basically undoes the work of sympathetic division. The parasympathetic nervous system slows respiration and heart rate while speeding up digestion. Stimulation of the parasympathetic nervous system results in the following given below :

• Contraction of pupils

• Lower heart rate and blood pressure

• Improved digestion

• Increased saliva and mucus production

• Urine secretion increases

Parasympathetic Nervous System Function

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Your PSNS originates in your brain and spreads out through long fibres that connect with special neurons near the organ on which they intend to act. Once PSNS signals reach these neurons, they travel only a short distance to their respective organs. Examples of the areas the PSNS acts on include the following:

• eyes

• lacrimal glands are responsible for producing tears

• parotid glands are responsible for producing produce saliva

• salivary glands responsible for producing saliva

• nerves in the stomach as well as trunk

• nerves that go to the bladder

• nerves as well as blood vessels responsible for the male erection

The PSNS is a "business as usual" system that keeps your body's basic functions functioning normally.

Parasympathetic Nerves

The cranial nerves are known as paired nerves and these nerves are responsible for many movements and sensations that take place in your body’s head and neck. The nerves all start in the brain. There are a total of 12 cranial nerves labelled using Roman numerals from I to XII, with the first set of nerves located at the brain’s front.

Major Cranial Nerves

• III. Oculomotor nerve is the nerve that aids in constricting the pupil, making it appear smaller.

• VII. Facial nerve is the nerve that regulates saliva and mucus secretions in the mouth and nose, respectively.

• IX. Glossopharyngeal nerve is the nerve that connects to the parotid salivary glands, which produce extra saliva for the tongue and elsewhere.

• X. Vagus nerve. This nerve is responsible for an estimated 75% of all parasympathetic nerve fibres in the body. The stomach, kidneys, liver, pancreas, gallbladder, bladder, anal sphincter, vagina, and penis all have branches from this nerve.

Parasympathetic Stimulation - The Parasympathetic Nervous System and the Vagus Nerve

There is no conversation about the parasympathetic nervous system which is complete without mentioning the vagus nerve.

The vagus nerve is the longest in the autonomic nervous system, reaching nearly every major system in the body. It also serves as the primary component of the parasympathetic nervous system. That is why vagus nerve stimulation (VNS) is known to be an excellent way to activate the parasympathetic nervous system and aid in relaxation.

Examples of Parasympathetic Activity and Responses

The term SLUDD is an easy acronym to remember how and where the PSNS works. This abbreviation stands for the following:

• Salivation: As part of its rest-and-digest function, the PSNS stimulates saliva production, which contains enzymes that aid in food digestion.

• Lacrimation: Lacrimation is a fancy term for crying. Tears lubricate your eyes, protecting their delicate tissues.

• Urination: The PSNS contracts the bladder, causing it to squeeze and urine to escape.

• Digestion: The PSNS stimulates saliva production to aid digestion. It also causes peristalsis, or the movement of the stomach and intestines to digest food and release bile to allow the body to digest fats.

• Defecation: The PSNS constricts the sphincters in the intestine and moves digested food material down the digestive tract, allowing a person to have proper bowel movements.

Parasympathetic Fibers 

The parasympathetic nervous system derives its nerve fibres from the central nervous system. Several cranial nerves, including the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve, are examples of specific nerves. Three sacral spinal nerves (S2-4), also known as the pelvic splanchnic nerves, function as parasympathetic nerves.

The parasympathetic nervous system exits the central nervous system via cranial nerves (CN) III, VII, IX, and X. The vagus nerves (CN-X) contain approximately 80% or more of all parasympathetic nerve fibres, which pass to the heart, lungs, oesophagus, stomach, and small intestine, the proximal half of the colon, the liver, gallbladder, pancreas, as well as the upper portions of the colon and ureters.

The vagus nerves (CN-X) contain approximately 80% or more of all parasympathetic nerve fibres, which pass to the heart, lungs, oesophagus, stomach, and small intestine, the proximal half of the colon, the liver, gallbladder, pancreas, as well as the upper portions of the ureters.