Parasympathetic nervous system
Overview
The parasympathetic nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

(PSNS) is one of the two main divisions of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 (ANS). The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously. To be specific, the parasympathetic system is responsible for stimulation of "rest-and-digest" activities that occur when the body is at rest, including sexual arousal, salivation, lacrimation
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....

 (tears), urination
Urination
Urination, also known as micturition, voiding, peeing, weeing, pissing, and more rarely, emiction, is the ejection of urine from the urinary bladder through the urethra to the outside of the body. In healthy humans the process of urination is under voluntary control...

, digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

, and defecation
Defecation
Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...

. Its action is described as being complementary to that of one of the other main branches of the ANS, the sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

, which is responsible for stimulating activities associated with the fight-or-flight response
Fight-or-flight response
The fight-or-flight response was first described by Walter Bradford Cannon....

.
Sympathetic
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

 and parasympathetic divisions typically function in opposition to each other.
Encyclopedia
The parasympathetic nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

(PSNS) is one of the two main divisions of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 (ANS). The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously. To be specific, the parasympathetic system is responsible for stimulation of "rest-and-digest" activities that occur when the body is at rest, including sexual arousal, salivation, lacrimation
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....

 (tears), urination
Urination
Urination, also known as micturition, voiding, peeing, weeing, pissing, and more rarely, emiction, is the ejection of urine from the urinary bladder through the urethra to the outside of the body. In healthy humans the process of urination is under voluntary control...

, digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

, and defecation
Defecation
Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...

. Its action is described as being complementary to that of one of the other main branches of the ANS, the sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

, which is responsible for stimulating activities associated with the fight-or-flight response
Fight-or-flight response
The fight-or-flight response was first described by Walter Bradford Cannon....

.

Relation to sympathetic nervous system

Sympathetic
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

 and parasympathetic divisions typically function in opposition to each other. This natural opposition is better understood as complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake. The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. A useful acronym to summarize the functions of the parasympathetic nervous system is SLUDD (saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

tion, lacrimation
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....

, urination
Urination
Urination, also known as micturition, voiding, peeing, weeing, pissing, and more rarely, emiction, is the ejection of urine from the urinary bladder through the urethra to the outside of the body. In healthy humans the process of urination is under voluntary control...

, digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

, and defecation
Defecation
Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...

).

Physical location

The parasympathetic nerves (PSNS) are autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 (aka "visceral") branches of the peripheral nervous system
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

 (PNS). Parasympathetic nerve fibers arise from the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 with the S2, S3, and S4 spinal nerve
Spinal nerve
The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body...

s and from the third
Oculomotor nerve
The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...

, seventh
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

, ninth
Glossopharyngeal nerve
The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...

, and tenth
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...

 cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...

. Because of its location, the parasympathetic system is commonly referred to as having "craniosacral outflow", which stands in contrast to the sympathetic nervous system, which is said to have "thoracolumbar outflow".

The parasympathetic nerves that arise from the S2, S3, and S4 spinal nerves are commonly referred to as the pelvic splanchnic nerves
Pelvic splanchnic nerves
Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the hindgut.-Structure:...

 or the "nervi erigentes".

Pathways

As is true in the sympathetic nervous system, efferent
Efferent nerve
In the nervous system, efferent nerves, otherwise known as motor or effector neurons, carry nerve impulses away from the central nervous system to effectors such as muscles or glands...

 parasympathetic nerve signals are carried from the central nervous system to their targets by a system of two neurons. The first neuron in this pathway is referred to as the preganglionic or presynaptic neuron. Its cell body sits in the central nervous system and its axon usually extends to a ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....

 somewhere else in the body where it synapses with the dendrites of the second neuron in the chain. This second neuron is referred to as the postganglionic or postsynaptic neuron.

The axons of presynaptic parasympathetic neurons are usually long: They extend from the CNS into a ganglion that is either very close to or embedded in their target organ. As a result, the postsynaptic parasympathetic nerve fibers are very short.

In the cranium, preganglionic PSN (CN III, CN VII, and CN IX) usually arise from specific nuclei in the Central Nervous System
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 (CNS) and synapse at one of four parasympathetic ganglia
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....

: ciliary
Ciliary ganglion
The ciliary ganglion is a parasympathetic ganglion located in the posterior orbit. It measures 1–2 millimeters in diameter and contains approximately 2,500 neurons. Preganglionic axons from the Edinger-Westphal nucleus travel along the oculomotor nerve and form synapses with these cells...

, pterygopalatine
Pterygopalatine ganglion
The pterygopalatine ganglion is a parasympathetic ganglion found in the pterygopalatine fossa. It is one of four parasympathetic ganglia of the head and neck....

, otic
Otic ganglion
The otic ganglion is a small, oval shaped, flattened parasympathetic ganglion of a reddish-gray color, located immediately below the foramen ovale in the infratemporal fossa. It gives innervation to the parotid gland for salivation....

, or submandibular
Submandibular ganglion
The submandibular ganglion is part of the human autonomic nervous system. It is one of four parasympathetic ganglia of the head and neck...

. From these four ganglia the PSN complete their journey to target tissues via CN V (trigeminal) branches (ophthalmic nerve
Ophthalmic nerve
The ophthalmic nerve is one of the three branches of the trigeminal nerve, the fifth cranial nerve. The ophthalmic nerve carries only sensory fibers.-Branches:*Nasociliary nerve**sensory root of ciliary ganglion**posterior ethmoidal nerve...

 CN V1, maxillary nerve CN V2, mandibular nerve
Mandibular nerve
The mandibular nerve is the largest of the three branches of the trigeminal nerve.-Roots:It is made up of two roots:* a large sensory root proceeding from the inferior angle of the trigeminal ganglion....

 CN V3).

The vagus nerve (CN X) does not participate in these cranial ganglia as most of its PSN fibers are destined for a broad array of ganglia on or near thoracic viscera (esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

, trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

, heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

, lungs) and abdominal viscera (stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

, pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

, liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, kidneys). It travels all the way down to the midgut/hindgut junction, which occurs just before the splenic flexure
Splenic flexure
The splenic flexure is a sharp bend between the transverse and the descending colon in the left upper quadrant of humans. The left colic flexure is near the spleen, and hence called the splenic flexure. There are two colic flexures in the transverse colon — the other being the hepatic...

 of the transverse colon
Transverse colon
The transverse colon, the longest and most movable part of the colon, passes with a downward convexity from the right hypochondrium region across the abdomen, opposite the confines of the epigastric and umbilical zones, into the left hypochondrium region, where it curves sharply on itself beneath...

 at "Cannon-Böhm point".

The pelvic splanchnic efferent preganglionic nerve cell bodies
Pelvic splanchnic nerves
Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the hindgut.-Structure:...

 reside in the lateral gray horn
Intermediolateral nucleus
The intermediolateral nucleus is a region of gray matter found in Rexed lamina VII of the spinal column.Rexed Lamina VII contains several well defined nuclei including the nucleus dorsalis , the intermediolateral cell column , and the sacral autonomic nucleus.It extends from the first thoracic...

 of the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

 at the S2-S4 spinal levels. Their axons continue away from the CNS to synapse at an autonomic ganglion. The PSN ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....

 where these preganglionic neurons synapse will be close to the organ of innervation. This differs from the sympathetic nervous system, where synapses between pre- and post-ganglionic efferent nerves in general occur at ganglia that are farther away from the target organ.

Sensation

The afferent fibers of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

, which transmit sensory information from the internal organs of the body back to the central nervous system, are not divided into parasympathetic and sympathetic fibers as the efferent fibers are. Instead, autonomic sensory information is conducted by general visceral afferent fibers
General visceral afferent fibers
The general visceral afferent fibers conduct sensory impulses from the viscera, glands, and blood vessels to the central nervous system. They are considered to be part of the autonomic nervous system...

.

General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS. While the unconscious reflex arcs normally are undetectable, in certain instances they may send pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...

 sensations to the CNS masked as referred pain
Referred pain
Referred pain is pain perceived at a location other than the site of the painful stimulus. An example is the case of ischemia brought on by a myocardial infarction , where pain is often felt in the neck, shoulders, and back rather than in the chest, the site of the injury...

. If the peritoneal cavity
Peritoneal cavity
The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall...

 becomes inflamed or if the bowel is suddenly distended, the body will interpret the afferent pain stimulus as somatic
Somatic nervous system
The somatic nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles...

 in origin. This pain is usually non-localized. The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

.

Cranial Nerve Parasympathetic Paths and Control

The oculomotor nerve
Oculomotor nerve
The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...

 is responsible for several parasympathetic functions related to the eye. The oculomotor PNS fibers originate in the Edinger-Westphal nucleus
Edinger-Westphal nucleus
The Edinger-Westphal nucleus is the accessory parasympathetic cranial nerve nucleus of the oculomotor nerve , supplying the constricting muscles of the iris...

 in the CNS and travel through the superior orbital fissure to synapse in the ciliary ganglion
Ciliary ganglion
The ciliary ganglion is a parasympathetic ganglion located in the posterior orbit. It measures 1–2 millimeters in diameter and contains approximately 2,500 neurons. Preganglionic axons from the Edinger-Westphal nucleus travel along the oculomotor nerve and form synapses with these cells...

 located just behind the orbit (eye). From the ciliary ganglion the postganglionic PSN fibers leave via short ciliary nerve fibers, a continuation of the nasociliary nerve
Nasociliary nerve
The nasociliary nerve is a branch of the ophthalmic nerve. It is intermediate in size between the two other main branches of the ophthalmic nerve, the frontal nerve and the lacrimal nerve, and is more deeply placed.-Path:...

 (a branch of ophthalmic division of the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

, CN V1). The short ciliary nerves innervate the orbit to control the ciliary muscle (responsible for accommodation
Accommodation (eye)
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image on an object as its distance changes....

) and the sphincter pupillae muscle, which is responsible for miosis or constriction of the pupil (in response to light or accommodation).

The parasympathetic aspect of the facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

 (CN VII) controls secretion of the sublingual and submandibular salivary glands, the lacrimal gland
Lacrimal gland
The lacrimal glands are paired almond-shaped glands, one for each eye, that secrete the aqueous layer of the tear film. They are situated in the upper, outer portion of each orbit, in the lacrimal fossa of the orbit formed by the frontal bone. Inflammation of the lacrimal glands is called...

, and the glands associated with the nasal cavity. The preganglionic fibers originate within the CNS in the superior salivatory nucleus and leave as the intermediate nerve (which some consider a separate cranial nerve altogether) to connect with the facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

 just distal (further out) to it surfacing the CNS. Just after the facial nerve geniculate ganglion
Geniculate ganglion
The geniculate ganglion is an L-shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head...

 (general sensory ganglion) in the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...

, the facial nerve gives off two separate parasympathetic nerves. The first is the greater petrosal nerve and the second is the chorda tympani
Chorda tympani
The chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the Stylomastoid foramen...

. The greater petrosal nerve travels through the middle ear and eventually combines with the deep petrosal nerve (sympathetic fibers) to form the nerve of the pterygoid canal
Pterygoid canal
The pterygoid canal is a passage in the skull leading from just anterior to the foramen lacerum in the middle cranial fossa to the pterygopalatine fossa.-Structure:...

. The PSN fibers of the nerve of the pterygoid canal synapse at the pterygopalatine ganglion
Pterygopalatine ganglion
The pterygopalatine ganglion is a parasympathetic ganglion found in the pterygopalatine fossa. It is one of four parasympathetic ganglia of the head and neck....

, which is closely associated with the maxillary division of the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

 (CN V2). The postganglionic PSN fibers leave the pterygopalatine ganglion in several directions. One division leaves on the zygomatic division of CN V2 and travels on a communicating branch to unite with the lacrimal nerve (branch of the ophthalmic nerve of CN V1) before synapsing at the lacrimal gland. These PSN to the lacrimal gland control tear production.

A separate group of PSN leaving from the pterygopalatine ganglion are the descending palatine nerves
Palatine nerves
The palatine nerves are distributed to the roof of the mouth, soft palate, tonsil, and lining membrane of the nasal cavity.Most of their fibers are derived from the sphenopalatine branches of the maxillary nerve....

 (CN V2 branch), which include the greater and lesser palatine nerves. The greater palatine PSN synapse on the hard palate and regulate mucus glands located there. The lesser palatine nerve synapses at the soft palate and controls sparse taste receptors and mucus glands. Yet another set of divisions from the pterygopalatine ganglion are the posterior, superior, and inferior lateral nasal nerves; and the nasopalatine nerves (all branches of CN V2, maxillary division of the trigeminal nerve) that bring PSN to glands of the nasal mucosa. The second PSN branch that leaves the facial nerve is the chorda tympani. This nerve carries secretomotor
Secretomotor
Secretomotor refers to the capacity of a structure to induce a gland to secrete a substance .Secretomotor nerve endings are frequently contrasted with sensory neuron endings and motor nerve endings. An example of secretomotor activity can be seen with the lacrimal gland, which secretes the aqueous...

 fibers to the submandibular
Submandibular gland
The paired submandibular glands are salivary glands located beneath the floor of the mouth. In humans, they account for 70% of the salivary volume and weigh about 15 grams. Unstimulated in humans, the percentage contribution to whole saliva; ~25% Parotid, Submandibular and Sublingual ~ 67% and...

 and sublingual
Sublingual gland
The sublingual glands are salivary glands in the mouth.They lie anterior to the submandibular gland under the tongue, beneath the mucous membrane of the floor of the mouth.They are drained by 8-20 excretory ducts called the ducts of Rivinus....

 glands. The chorda tympani travels through the middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...

 and attaches to the lingual nerve
Lingual nerve
The lingual nerve is a branch of the mandibular nerve , itself a branch of the trigeminal nerve, which supplies sensory innervation to the tongue...

 (mandibular division of trigeminal, CN V3). After joining the lingual nerve, the preganglionic fibers synapse at the submandibular ganglion and send postganglionic fibers to the sublingual and submandibular salivary glands.

The glossopharyngeal nerve, CNIX, has parasympathetic fibers that innervate the parotid salivary gland. The preganglionic fibers depart CNIX as the tympanic nerve
Tympanic nerve
The tympanic nerve is a branch of the glossopharyngeal nerve found near the ear.-Path:It arises from the petrous ganglion, and ascends to the tympanic cavity through a small canal, the fossula petrosa/tympanic canaliculus, on the under surface of the petrous portion of the temporal bone on the...

 and continue to the middle ear where they make up a tympanic plexus on the cochlear promontory of the mesotympanum. The tympanic plexus of nerves rejoin and form the lesser petrosal nerve
Lesser petrosal nerve
The lesser petrosal nerve consists of parasympathetic fibres. It leaves the tympanic plexus to synapse in the otic ganglion, and eventually provide parasympathetic innervation to the parotid gland....

 and exit through the foramen ovale
Foramen ovale (skull)
At the base of the skull the foramen ovale is one of the larger of the several holes that transmit nerves through the skull. The foramen ovale is situated in the posterior part of the sphenoid bone, posterolateral to the foramen rotundum.-Contents:Several nerves, arteries and veins pass through...

 to synapse at the otic ganglion
Otic ganglion
The otic ganglion is a small, oval shaped, flattened parasympathetic ganglion of a reddish-gray color, located immediately below the foramen ovale in the infratemporal fossa. It gives innervation to the parotid gland for salivation....

. From the otic ganglion postganglionic parasympathetic fibers travel with the auriculotemporal nerve (mandibular branch of trigeminal, CN V3) to the parotid salivary gland.

The vagus nerve, named from the Latin word vagus means literally "Wandering", since the nerve controls such a broad range of target tissues, has PSN that originate in the dorsal nucleus of the vagus nerve and the nucleus ambiguus
Nucleus ambiguus
The nucleus ambiguus is a region of histologically disparate cells located just dorsal to the inferior olivary nucleus in the lateral portion of the upper medulla...

 in the CNS. The vagus nerve is an unusual cranial PSN in that it doesn't join the trigeminal nerve in order to get to its target tissues. Another peculiarity is that the vagus has an autonomic ganglion
Autonomic ganglion
Autonomic ganglia are clusters of neuronal cell bodies and their dendrites and are essentially a junction between autonomic nerves originating from the central nervous system and autonomic nerves innervating their target organs in the periphery....

 associated with it at approximately the level of C1 vertebra. The vagus gives no PSN to the cranium. The vagus nerve is hard to track definitively due to its ubiquitous nature in the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

 and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 so the major contributions will be discussed. Several PSN nerves come off the vagus nerve as it enters the thorax. One nerve is the recurrent laryngeal nerve
Laryngeal nerve
The laryngeal nerve, or Galen's nerve, is a nerve originating from the vagus nerve. It comprises two branches, the cranial superior laryngeal nerve, which leaves the vagus at the distal ganglion and passes ventrally to the larynx supplying the cricothyroid muscle and laryngeal mucosa, and the...

, which becomes the inferior laryngeal nerve. From the left vagus nerve the recurrent laryngeal nerve hooks around the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...

 to travel back up to the larynx and proximal esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

 while, from the right vagus nerve, the recurrent laryngeal nerve hooks around the right subclavian artery
Subclavian artery
In human anatomy, the subclavian arteries are two major arteries of the upper thorax , below the clavicle . They receive blood from the top of the aorta...

 to travel back up to the same location as its counterpart. These different paths are a direct result of embryological development of the circulatory system. Each recurrent laryngeal nerve supplies the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

 and the esophagus with parasympathetic secretomotor
Secretomotor
Secretomotor refers to the capacity of a structure to induce a gland to secrete a substance .Secretomotor nerve endings are frequently contrasted with sensory neuron endings and motor nerve endings. An example of secretomotor activity can be seen with the lacrimal gland, which secretes the aqueous...

 innervation for glands associated with them (and other fibers that are not PSN).

Another nerve that comes off the vagal nerves approximately at the level of entering the thorax are the cardiac nerves. These cardiac nerves go on to form cardiac and pulmonary plexuses around the heart and lungs. As the main vagus nerves continue into the thorax they become intimately linked with the esophagus and sympathetic nerves from the sympathetic trunks to form the esophageal plexus. This is very efficient as the major function of the vagus nerve from there on will be control of the gut smooth muscles and glands. As the esophageal plexus
Esophageal plexus
The esophageal plexus is formed by fibers from two sources: 1.branches of the vagus nerve 2.visceral branches of the sympathetic trunk. The esophageal plexus and the cardiac plexus contain the same types of fibers and are both considered thoracic autonomic plexus.-Parasympathetic Fibers:1. The...

 enter the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 through the esophageal hiatus
Esophageal hiatus
In human anatomy, the esophageal hiatus is a hole in the diaphragm through which the esophagus passes. It is located in the right crus of the diaphragm.It is located approximately at level of the tenth thoracic vertebra ....

 anterior and posterior vagal trunks form. The vagal trunks then join with preaortic sympathetic ganglion around the aorta to disperse with the blood vessels and sympathetic nerves throughout the abdomen. The extent of the PSN in the abdomen include the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

, kidneys, liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, gall bladder, stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

 and gut
Gut (zoology)
In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...

 tube. The vagal contribution of PSN continues down the gut tube until the end of the midgut
Midgut
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop"...

. The midgut ends 2/3 of the way across the transverse colon near the splenic flexure
Splenic flexure
The splenic flexure is a sharp bend between the transverse and the descending colon in the left upper quadrant of humans. The left colic flexure is near the spleen, and hence called the splenic flexure. There are two colic flexures in the transverse colon — the other being the hepatic...

.

Pelvic Splanchnic Control

The pelvic splanchnic nerves, S2-4, work in tandem to innervate the pelvic viscera. Unlike in the cranium, where one PSN was in charge of one particular tissue or region, for the most part the pelvic splanchnics each contribute fibers to pelvic viscera by first traveling to one or more plexuses before being dispersed to the target tissue. These plexuses are composed of mixed autonomic nerve fibers (PSN and SN) and include the vesical, prostatic, rectal, uterovaginal, and inferior hypogastric plexus. The preganglionic neurons in the neurons do not synapse in named ganglion as in the cranium but rather in the walls of the tissues or organs that they innervate. The fiber paths are variable and each individual's autonomic nervous system in the pelvis is unique. The visceral tissues in the pelvis that the PSN control include: urinary bladder, ureters, urinary sphincter, anal sphincter, uterus, prostate, glands, vagina and penis. Unconsciously, the PSN will cause peristaltic movements of the ureters helping to move urine from the kidneys into the bladder and move feces down the intestinal tract and upon necessity, the PSN will assist excreting urine from the bladder or defecation. Stimulation of the PSN will cause the detrusor muscle (urinary bladder wall) to contract and simultaneously relax the internal sphincter urethrae muscle to relax allowing void of urine. Also, PSN stimulation to the internal anal sphincter will relax this muscle and allow defecation. There are other skeletal muscles involved with these processes but the PSN play a huge role in continence.

Another role that the PSN play in the pelvis is in sexual activity. In males, the cavernous nerves from the prostatic plexus stimulate smooth muscle in the fibrous trabeculae of the coiled helicene
Helicene
Helicenes in organic chemistry are ortho-condensed polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped molecules...

 arteries to relax and allow blood to fill the corpora cavernosum and the corpus spongiosum of the penis, making it rigid to prepare for sexual activity. Upon emission of ejaculate, the sympathetics participate and cause peristalsis of the ductus deferens and closure of the internal urethral sphincter to prevent semen from entering the bladder. At the same time, parasympathetics cause peristalsis of the urethral muscle, and the pudendal nerve causes contraction of the bulbospongiosus (skeletal muscle is not via PSN), to forcibly emit the semen. During remission the penis becomes flaccid again. In the female, there is erectile tissue analogous to the male yet less substantial that plays a large role in sexual stimulation. The PSN cause release of secretions in the female that decrease friction. Also in the female, the parasympathetics innervate the fallopian tubes, which helps peristaltic contractions and movement of the oocyte to the uterus for implantation. The secretions from the female genital tract aids in semen migration. The PSN (and SN to a lesser extent) play a huge role in reproduction.

Clinical Significance

The parasympathetic nervous system promotes digestion and the synthesis of glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

, and allows for normal function and behavior.

Receptors

The parasympathetic nervous system uses chiefly acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...

 (ACh) as its neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

, although other peptides (such as cholecystokinin
Cholecystokinin
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...

) may act on the PSNS as a neurotransmitter. The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic
Cholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...

 receptors. Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of postganglionic neurons. The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.

Types of muscarinic receptors

The five main types of muscarinic receptors:
  • The M1 muscarinic receptors
    Muscarinic acetylcholine receptor M1
    The muscarinic acetylcholine receptor M1, also known as the cholinergic receptor, muscarinic 1, is a muscarinic receptor.This receptor is found mediating slow EPSP at the ganglion in the postganglionic nerve, is common in exocrine glands and in the CNS.It is predominantly found bound to G proteins...

      are located in the neural system.

  • The M2 muscarinic receptors
    Muscarinic acetylcholine receptor M2
    The muscarinic acetylcholine receptor M2, also known as the cholinergic receptor, muscarinic 2, is a muscarinic acetylcholine receptor.-Heart:...

      are located in the heart, and act to bring the heart back to normal after the actions of the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the sinoatrial node
    Sinoatrial node
    The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...

     (SA node) and atrioventricular node
    Atrioventricular node
    The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...

     (AV node). Note, they have a minimal effect on the contractile forces of the ventricular muscle due to sparse innervation of the ventricles from the parasympathetic nervous system.

  • The M3 muscarinic receptors
    Muscarinic acetylcholine receptor M3
    The muscarinic acetylcholine receptor M3, also known as the cholinergic receptor, muscarinic 3, is a muscarinic acetylcholine receptor. It is encoded by the human gene CHRM3....

      are located at many places in the body, such as the endothelial cells of blood vessels, as well as the lungs causing bronchoconstriction
    Bronchoconstriction
    Bronchoconstriction is the constriction of the airways in the lungs due to the tightening of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Bronchoconstriction can also be due to an accumulation of thick mucus....

    . The net effect of uninnervated M3 receptors on blood vessels is vasodilation
    Vasodilation
    Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...

    , as acetylcholine causes endothelial cells to produce nitric oxide, which diffuses to smooth muscle and results in vasodilation. They are also in the smooth muscles of the gastrointestinal tract
    Gastrointestinal tract
    The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

     (GIT), which help in increasing intestinal motility and dilating sphincters. The M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body. They are also located on the detrusor muscle of the bladder, causing contraction of the bladder.

  • The M4 muscarinic receptors
    Muscarinic acetylcholine receptor M4
    The muscarinic acetylcholine receptor M4, also known as the cholinergic receptor, muscarinic 4 , is a protein that, in humans, is encoded by the CHRM4 gene.-Function:...

    : Postganglionic cholinergic nerves, possible CNS effects

  • The M5 muscarinic receptors
    Muscarinic acetylcholine receptor M5
    The human muscarinic acetylcholine receptor M5 which is encoded by the gene is a member of the G protein-coupled receptor superfamily of integral membrane proteins. Binding of the endogenous ligand acetylcholine to the M5 receptor triggers a number of cellular responses such as adenylate cyclase...

    : Possible effects on the CNS

External links

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