Author: Gordana Sendic•Reviewer: Alexandru Andrușca MD, PhDLast reviewed: September 09, 2021Reading time: 11 minutes

Parasympathetic nervous system anatomy

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

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

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This article will talk about the anatomy and functions that the parasympathetic concerned system.

Key facts about the parasympathetic nervous 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, little intestine, proximal huge intestine
Sacral outflowPelvic splanchnic nerves – to decrease colon, sigmoid colon, rectum, bladder, penis or clitoris

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The parasympathetic concerned system consists of many pathways that connect its craniosacral materials with the peripheral tissues. Every parasympathetic pathway is composed of 2 neurons, the presynaptic (preganglionic) and also postsynaptic (postganglionic) neurons, which are linked by the axons that the presynaptic neurons.

The presynaptic neurons of the parasympathetic device are located within the medulla oblongata and also sacral spinal cord. They offer off long axons (presynaptic fibers) the leave the CNS and travel in the direction of the postsynaptic neurons. When they reach them, the presynaptic fibers synapse with the bodies of the postsynaptic neurons. This synapse supplies the acetylcholine as a neurotransmitter, i m sorry is why the parasympathetic pathways are described as the cholinergic pathways. The presynaptic neurons that the parasympathetic pathways are situated within the two significant parts of the central nervous system:

The postsynaptic neurons are uncovered within the parasympathetic ganglia, which commonly lie close to or in ~ the target organs. After ~ receiving the advertise from the presynaptic neuron, the postsynaptic neuron conveys the neural impulse further down that axon (postsynaptic fiber). The postsynaptic fibers are significantly much shorter than the presynaptic ones, offered that the postsynaptic neuronal bodies lie in the near proximity of your target organs.

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Cranial part

The cranial part of the parasympathetic nervous system stems from the nuclei that the cranial nerves III, VII, IX and also X. The presynaptic yarn of these neurons join these cranial nerves in stimulate to reach the parasympathetic ganglia that the head. 

The cranial nerves that carry the cranial parasympathetic outflow room the following:


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

Vagus nerve


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

The presynaptic parasympathetic yarn of the vagus nerve originate native the dorsal cell core of vagus nerve and the cell core ambiguus in the brainstem. The presynaptic fibers take trip within the vagus nerve come reach countless parasympathetic ganglia around and also within the guts of the thorax and abdomen. Top top synapsing, the ganglia project brief postsynaptic fibers, which then innervate the target organs. 

The fibers stemming indigenous the dorsal cell core of the vagus nerve mainly innervate the frameworks of the lungs and also gastrointestinal tract as much as the splenic flexure of the large intestine, if the fibers from the nucleus ambiguus supply the smooth musculature the the heart, pharynx, larynx and also soft palate. 

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

Learn much more about the vagus nerve with our articles, videos, quizzes and also labelled diagrams.

Vagus nerve discover study unit

Sacral part

The presynaptic parasympathetic neurons of the sacral part of the PSNS lie in ~ the gray issue of the S2-S4 segments that the spinal cord. This fibers leaving the spinal cord with the anterior roots of the sacral spinal nerves S2-S4 and the pelvic splanchnic nerves that to happen from your anterior branches.

this fibers synapse with the parasympathetic ganglia about the descending and also sigmoid components of the colon, the rectum, and the viscera the the pelvic cavity. This ganglia then project the postsynaptic yarn which innervate the discussed organs.



The autonomic nervous system (ANS) controls and regulates the attributes of the visceral organs, smooth and also cardiac muscles and glands without any kind of conscious initiative of one individual, and is therefore referred to as involuntary. The ANS dram a critical role in the maintenance of homeostasis with the complementary attributes of its two anatomically and functionally unique divisions; the parasympathetic and also sympathetic nervous systems. Both systems provide some level of nervous input come a given tissue at all times. Each of them either increases or to reduce the activity of the innervated structure, complementing each other’s functions.

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Parasympathetic fibers are sent out to miscellaneous viscera come ensure various involuntary functions. In general, the is obvious that the cranial outflow gives parasympathetic innervation to the head, and the sacral outflow gives the parasympathetic innervations that the pelvic viscera. However, an estimated 75% of all parasympathetic outflow in the whole body originates from the vagus nerve, that offers the thoracic and abdominal viscera.

eyes (pupil)

The parasympathetic innervation brought through the oculomotor nerve outcomes in two occasions in the eye:

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

In addition, the parasympathetic stimulation of the pterygopalatine ganglion via the facial nerve reasons increased secretion of the lacrimal gland, result in raised tear production.

cradle tract

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


The parasympathetic outflow with the vagus nerve has actually a more direct result on digestion, boosting the release of cradle juices and enzymes from the stomach, pancreas and gallbladder and increasing the peristalsis the the cradle tract. The PNS likewise causes convulsion of the rectum and relaxation of the inner anal sphincter to permit defecation.

The vagus nerve innervates the abdominal viscera by developing the two plexuses along the entire length of the intestine;

Submucosal worried plexus (of Meissner) uncovered in the submucosa that the digestive tube and also contains just parasympathetic input from the vagus nerve (CN X).

Cardiorespiratory system


The parasympathetic outflow v the vagus nerve plays critical role in heart rate. The vagus nerve acts upon atrioventricular (AV) node, slowly its conduction and also thus slowly the love rate. 

Parasympathetic stimulation additionally relaxes the smooth musculature the the peripheral blood vessels, which outcomes in the vasodilation that peripheral vasculature. In comparison to this, acting on the smooth muscles of the coronary vessels, the parasympathetic nerves reason their vasoconstriction in response to reduced demand for oxygen. Acting on the lungs, the PSNS contract the smooth muscles of the tracheobronchial tree, bring about bronchoconstriction and promo of mucus secretion in the bronchi.

Genitourinary system

The sacral parasympathetic outflow acts upon the pelvic viscera. It reasons the be safe of the interior sphincter that urinary bladder and simultaneous convulsion of the detrusor muscle that the urinary bladder wall. This rises the intraluminal press within the bladder, in order to promoting urination. In addition, the PNS reasons stimulation that erectile organization of the exterior genitalia, permitting an erection of the penis/clitoris to occur. 

Clinical correlation

Diabetic cardiac autonomic neuropathy is a serious and also common complication the diabetes mellitus that is often under-diagnosed however can lead to severe morbidity and also mortality, as result of the connected cardiovascular burden. In the early periods the this condition, over there is degeneration of the sympathetic regulate of the heart, which is adhered to in later stages by the degeneration that the parasympathetic stimulation that the heart. Also, its results on the parasympathetic nervous mechanism cause several cardiovascular disturbances, consisting of resting tachycardia, exercise intolerance and postural hypotension.

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