Author: Gordana Sendic•Reviewer: Alexandru Andrușca MD, PhDLast reviewed: October 04, 2021Reading time: 13 minutes

Parasympathetic nervous mechanism anatomy

The parasympathetic nervous system (PSNS) is a division of the autonomic nervous system (ANS) that controls the activity of the smooth and also cardiac muscles and also glands. It functions in synergy through the forgiveness nervous system (SNS), i m sorry complements the PSNS activity. The parasympathetic nervous mechanism is also called the craniosacral division of the ANS, as its central nervous system components are located within the mind and the sacral section of the spinal cord.

The functions of the PNS are commonly described together the “rest and also digest” response, because it is connected in slowing under the love rate, be sure the sphincter muscle in the gastrointestinal and urinary tracts and also increasing intestinal and gland activity. The final an outcome is conserving energy and regulating an easy bodily features such together digestion and also urination. It is contrasted come the sympathetic concerned system, i beg your pardon is described as the “fight and flight” response that occurs in stressful situations and also has largely opposite functions.

You are watching: This division can also be called the craniosacral division.

This short article will talk about the anatomy and also functions of the parasympathetic nervous system.

Key facts around the parasympathetic worried system
Cranial outflowOculomotor nerve (CN III) – iris, ciliary musclesFacial nerve (CN VII) – lacrimal, nasal, palatine, pharyngeal, sublingual, submandibular glandsGlossopharyngeal nerve (CN IX) – parotid gland
Vagus outflowVagus nerve (CN X) – heart, larynx, trachea, bronchi, lungs, liver, gallbladder, stomach, pancreas, kidney, small intestine, proximal huge intestine
Sacral outflowPelvic splanchnic nerves – diminish colon, sigmoid colon, rectum, bladder, cock or clitoris

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The parasympathetic worried system consists of countless pathways that connect its craniosacral components with the peripheral tissues. Every parasympathetic pathway is composed of two neurons, the presynaptic (preganglionic) and also postsynaptic (postganglionic) neurons, which are linked by the axons that the presynaptic neurons.

The presynaptic neurons the the parasympathetic system are situated within the medulla oblongata and sacral spinal cord. They give off lengthy axons (presynaptic fibers) the leave the CNS and also travel towards the postsynaptic neurons. When they reach them, the presynaptic fibers synapse with the body of the postsynaptic neurons. This synapse uses the acetylcholine together a neurotransmitter, i beg your pardon is why the parasympathetic pathways are referred to as the cholinergic pathways. The presynaptic neurons that the parasympathetic pathways are situated within the two significant parts the the central nervous system:

The postsynaptic neurons are discovered within the parasympathetic ganglia, which typically lie near or within the target organs. ~ receiving the advertise from the presynaptic neuron, the postsynaptic neuron conveys the neural impulse additional down that is axon (postsynaptic fiber). The postsynaptic fibers are significantly much shorter than the presynaptic ones, provided that the postsynaptic neuronal body lie in the close proximity of their target organs.

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Cranial part

The cranial part of the parasympathetic nervous device stems from the nuclei the the cranial nerves III, VII, IX and X. The presynaptic yarn of this neurons join these cranial nerves in bespeak to with the parasympathetic ganglia that the head. 

The cranial nerves that bring the cranial parasympathetic outflow space the following:


Facial nerve (CN VII): dead presynaptic parasympathetic fibers from the superior salivatory nucleus and also synapses through the postsynaptic neurons discovered in the pterygopalatine and submandibular ganglia. This ganglia then job postsynaptic yarn via two nerves;

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The vagus nerve (CN X) is functionally not contained in the cranial parasympathetic outflow because it gives no parasympathetic innervation because that the head. Instead, it provides the parasympathetic innervation to the thoracic and ab viscera. 

The presynaptic parasympathetic yarn of the vagus nerve originate indigenous the dorsal cell nucleus of vagus nerve and the cell nucleus ambiguus in the brainstem. The presynaptic fibers take trip within the vagus nerve come reach numerous parasympathetic ganglia around and within the organs of the thorax and also abdomen. ~ above synapsing, the ganglia project brief postsynaptic fibers, which climate innervate the target organs. 

The yarn stemming from the dorsal nucleus of the vagus nerve mostly innervate the structures of the lungs and gastrointestinal tract up to the splenic flexure the the large intestine, when the yarn from the cell nucleus ambiguus it is provided the smooth musculature the the heart, pharynx, larynx and soft palate. 

Branches that the vagus nerve that convey parasympathetic supply
Thorax Pharyngeal, exceptional laryngeal, recurrent laryngeal, superior and also inferior cardiac, anterior and posterior bronchial and also esophageal branches
Abdomen Gastric, celiac and hepatic branches

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Sacral part

The presynaptic parasympathetic neurons that the sacral component of the PSNS lie within the gray matter of the S2-S4 segments that the spinal cord. These fibers leave the spinal cord through the anterior roots of the sacral spinal nerves S2-S4 and also the pelvic splanchnic nerves that arise from your anterior branches.

this fibers synapse with the parasympathetic ganglia roughly the descending and sigmoid components of the colon, the rectum, and the viscera the the pelvic cavity. These ganglia then task the postsynaptic fibers which innervate the pointed out organs.



The autonomic nervous system (ANS) controls and regulates the attributes of the visceral organs, smooth and cardiac muscles and also glands without any kind of conscious effort of one individual, and also is for this reason referred to together involuntary. The ANS theatre a an essential role in the maintain of homeostasis through the complementary features of its two anatomically and also functionally unique divisions; the parasympathetic and sympathetic nervous systems. Both systems administer some level of nervous input come a offered tissue at all times. Every of them either boosts or to reduce the task of the innervated structure, complementing every other’s functions.

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Parasympathetic yarn are sent out to assorted viscera come ensure different involuntary functions. In general, the is evident that the cranial outflow offers parasympathetic innervation come the head, and the sacral outflow gives the parasympathetic innervations the the pelvic viscera. However, an estimated 75% of all parasympathetic outflow in the entirety body comes from the vagus nerve, that gives the thoracic and abdominal muscle viscera.

eye (pupil)

The parasympathetic innervation lugged through the oculomotor nerve results in two events in the eye:

The convulsion of the sphincter pupillae muscle, which leader to the constriction of the pupil (myosis). 

In addition, the parasympathetic stimulation of the pterygopalatine ganglion via the facial nerve causes increased secretion of the lacrimal gland, resulting in enhanced tear production.

gastrointestinal tract

The parasympathetic innervation carried through the facial and also glossopharyngeal nerves stimulates the secretion of the submandibular, sublingual and parotid glands. The final an outcome is increased salivation, which disclosure digestion.

The parasympathetic outflow through the vagus nerve has actually a more direct effect on digestion, enhancing the relax of cradle juices and also enzymes from the stomach, pancreas and gallbladder and increasing the peristalsis of the cradle tract. The PNS likewise causes convulsion of the rectum and relaxation the the inner anal sphincter to enable defecation.

The vagus nerve innervates the abdominal viscera by forming the 2 plexuses follow me the entire length the the intestine;

Submucosal worried plexus (of Meissner) found in the submucosa of the digestive tube and contains just parasympathetic input native the vagus nerve (CN X).

Cardiorespiratory system

The parasympathetic outflow with the vagus nerve plays crucial role in love rate. The vagus nerve acts on atrioventricular (AV) node, slowly its conduction and thus slowly the love rate. 

Parasympathetic stimulation likewise relaxes the smooth musculature of the peripheral blood vessels, which results in the vasodilation that peripheral vasculature. In comparison to this, acting on the smooth muscles of the coronary vessels, the parasympathetic nerves cause their vasoconstriction in solution to reduced need for oxygen. Acting on the lungs, the PSNS contracts the smooth muscle of the tracheobronchial tree, resulting in bronchoconstriction and promotion of mucus secretion in the bronchi.

Genitourinary system

The sacral parasympathetic outflow acts upon the pelvic viscera. It causes the relaxation of the interior sphincter of urinary bladder and also simultaneous contraction of the detrusor muscle the the urinary bladder wall. This rises the intraluminal pressure within the bladder, in order to promoting urination. In addition, the PNS causes stimulation the erectile organization of the outside genitalia, allowing an erection that the penis/clitoris come occur. 

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Clinical correlation

Diabetic cardiac autonomic neuropathy is a serious and common complication of diabetes mellitus the is frequently under-diagnosed but can cause severe morbidity and also mortality, because of the associated cardiovascular burden. In the beforehand periods that this condition, there is degeneration that the sympathetic control of the heart, which is complied with in later on stages by the degeneration that the parasympathetic stimulation that the heart. Also, its results on the parasympathetic nervous device cause several cardiovascular disturbances, consisting of resting tachycardia, exercise intolerance and postural hypotension.



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