Vagus nerve
Encyclopedia
The vagus nerve also called pneumogastric nerve or cranial nerve X, is the tenth of twelve (excluding CN0) paired cranial nerves
. Upon leaving the medulla
between the olivary nucleus and the inferior cerebellar peduncle, it extends through the jugular foramen
, then passing into the carotid sheath
between the internal carotid artery
and the internal jugular vein
down below the head, to the neck, chest and abdomen
, where it contributes to the innervation of the viscera. Besides output to the various organs in the body, the vagus nerve conveys sensory information about the state of the body's organs to the central nervous system
. 80-90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves communicating the state of the viscera to the brain.
The medieval Latin
word vagus means literally "Wandering" (the words vagrant
, vagabond
, and vague come from the same root). Sometimes the branches are spoken of in the plural and are thus called vagi (ˈ). The vagus is also called the pneumogastric nerve since it innervates both the lungs and the stomach.
The motor division of the vagus nerve is derived from the basal plate
of the embryo
nic medulla oblongata
, while the sensory division originates from the cranial neural crest
.
The vagus nerve includes axons which emerge from or converge onto three nuclei of the medulla:
The vagus runs posterior to the common carotid artery and internal jugular vein inside the carotid sheath.
between the internal and external carotid arteries, then passing posterolateral to the common carotid artery. The cell bodies of visceral afferent
fibers of the vagus nerve are located bilaterally in the inferior ganglion of the vagus nerve (nodose ganglia).
The right vagus nerve gives rise to the right recurrent laryngeal nerve, which hooks around the right subclavian artery and ascends into the neck between the trachea and esophagus. The right vagus then crosses anteriorly to the right subclavian artery and runs posterior to the superior vena cava and descends posterior to the right main bronchus and contributes to cardiac, pulmonary, and esophageal plexuses. It forms the posterior vagal trunk at the lower part of the esophagus and enters the diaphragm through the esophageal hiatus.
The left vagus nerve enters the thorax between left common carotid artery and left subclavian artery and descends on the aortic arch. It gives rise to the left recurrent laryngeal nerve, which hooks around the aortic arch to the left of the ligamentum arteriosum and ascends between the trachea and esophagus. The left vagus further gives off thoracic cardiac branches, breaks up into pulmonary plexus, continues into the esophageal plexus, and enters the abdomen as the anterior vagal trunk in the esophageal hiatus of the diaphragm.
The vagus nerve supplies motor parasympathetic fibers to all the organs except the suprarenal (adrenal) glands, from the neck
down to the second segment of the transverse colon
. The vagus also controls a few skeletal muscle
s, notable ones being:
This means that the vagus nerve is responsible for such varied tasks as heart rate
, gastrointestinal peristalsis
, sweating
, and quite a few muscle movements in the mouth, including speech (via the recurrent laryngeal nerve
) and keeping the larynx open for breathing (via action of the posterior cricoarytenoid muscle
, the only abductor of the vocal folds). It also has some afferent fibers that innervate the inner (canal) portion of the outer ear
, via the Auricular branch (also known as Alderman's nerve
) and part of the meninges
. This explains why a person may cough when tickled on the ear (such as when trying to remove ear wax with a cotton swab).
is controlled by the vagus nerve. To be specific, the vagus nerve acts to lower the heart rate
. The right vagus innervates the sinoatrial node. Parasympathetic hyperstimulation predisposes those affected to bradyarrhythmias. The left vagus when hyperstimulated predisposes the heart to atrioventricular (AV) blocks
.
At this location, neuroscientist Otto Loewi
first proved that nerves secrete substances called neurotransmitters, which have effects on receptors in target tissues. In his experiment, Loewi electrically stimulated the vagus nerve of a frog heart, which slowed the heart. Then he took the fluid from the heart and transferred it to a second frog heart without a vagus nerve. The second heart slowed down without an electrical stimulation. Loewi described the substance released by the vagus nerve as vagusstoff
, which was later found to be acetylcholine
.
Drugs that inhibit the muscarinic cholinergic receptor (anticholinergics) such as atropine
and scopolamine
are called vagolytic because they inhibit the action of the vagus nerve on the heart, gastrointestinal tract, and other organs. Anticholinergic drugs increase heart rate and are used to treat bradycardia
(slow heart rate) and asystole
, which is when the heart has no electrical activity.
(VNS) therapy using a pacemaker-like device implanted in the chest is a treatment used since 1997 to control seizure
s in epilepsy patients and has recently been approved for treating drug-resistant cases of clinical depression
. A non-invasive VNS device that stimulates an afferent branch of the vagus nerve is also being developed and will soon undergo trials.
Clinical trials are currently underway in Antwerp, Belgium using VNS for the treatment of tonal tinnitus
after a breakthrough study published in early 2011 by researchers at the University of Texas - Dallas showed successful tinnitus
suppression in rats when tones were paired with brief pulses of stimulation of the vagus nerve.
http://www.utdallas.edu/news/2011/1/13-8021_Findings-Show-Promise-in-Battle-Against-Tinnitus_article.html
VNS may also be achieved by one of the vagal maneuvers: holding the breath for a few seconds, dipping the face in cold water, coughing, or tensing the stomach muscles as if to bear down to have a bowel movement. Patients with supraventricular tachycardia
, atrial fibrillation
, and other illnesses may be trained to perform vagal maneuvers (or find one or more on their own).
Vagus nerve blocking (VBLOC) therapy is similar to VNS but used only during the day. In a six-month open-label trial
involving three medical centers in Australia, Mexico, and Norway, vagus nerve blocking has helped 31 obese participants lose an average of nearly 15 percent of their excess weight. A year-long 300-participant double-blind, phase II trial has begun.
Vagotomy
(cutting of the vagus nerve) is a now-obsolete therapy that was performed for peptic ulcer disease. Vagotomy is currently being researched as a less invasive alternative weight-loss procedure to gastric bypass surgery
. The procedure curbs the feeling of hunger and is sometimes performed in conjunction with putting bands on patients' stomachs, resulting in average weight loss of 43% at six months with diet and exercise.
One serious side-effect of a Vagotomy is a Vitamin B-12 deficiency later in life - i.e., 10 years - that is similar to pernicious anemia. As one gets older, the stomach produces less acid. The acid, and one of its components called Intrinsic Factor
, is needed to metabolize B-12 from food. The vagotomy reduces the acid that ultimately leads to the deficiency, which, if left untreated, causes nerve damage, tiredness, dementia, paranoia, and ultimately death.
massage, Valsalva maneuver
, or pain
from any cause, in particular, having blood drawn. When the circulatory changes are great enough, vasovagal syncope
results. Relative dehydration tends to amplify these responses.
Excessive activation of the vagal nerve during emotional stress, which is a parasympathetic overcompensation of a strong sympathetic nervous system response associated with stress, can also cause vasovagal syncope
because of a sudden drop in blood pressure and heart rate. Vasovagal syncope affects young children and women more than other groups. It can also lead to temporary loss of bladder control under moments of extreme fear.
Research has shown that women having had complete spinal cord injury
can experience orgasm
s through the vagus nerve, which can go from the uterus
, cervix
, and, it is presumed, the vagina
to the brain.
Liver - Insulin signaling activates the adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in the Arcuate nucleus
, decreases AgRP release, and through the vagus nerve, leads to decreased glucose production by the liver by decreasing gluconeogenic enzymes : Phosphoenolpyruvate carboxykinase
, Glucose 6-phosphatase
)
), and choking when drinking fluid. There is also loss of gag reflex. Uvula
deviates away from the side of lesion, and there is failure of palate
elevation.
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...
. Upon leaving the medulla
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
between the olivary nucleus and the inferior cerebellar peduncle, it extends through the jugular foramen
Jugular foramen
The jugular foramen is a large aperture in the base of the skull. It is located behind the carotid canal and is formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side....
, then passing into the carotid sheath
Carotid sheath
The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the vascular compartment of the neck. It is part of the deep cervical fascia of the neck, below the superficial cervical fascia meaning the subcutaneous adipose tissue immediately beneath the skin.The deep...
between the internal carotid artery
Internal carotid artery
In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....
and the internal jugular vein
Internal jugular vein
The two internal jugular veins collect the blood from the brain, the superficial parts of the face, and the neck.-Path:On both sides and at the base of the brain, the inferior petrosal sinus and the sigmoid sinus join to form the internal jugular vein...
down below the head, to the neck, chest 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...
, where it contributes to the innervation of the viscera. Besides output to the various organs in the body, the vagus nerve conveys sensory information about the state of the body's organs to 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...
. 80-90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves communicating the state of the viscera to the brain.
The medieval Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word vagus means literally "Wandering" (the words vagrant
Vagrancy (people)
A vagrant is a person in poverty, who wanders from place to place without a home or regular employment or income.-Definition:A vagrant is "a person without a settled home or regular work who wanders from place to place and lives by begging;" vagrancy is the condition of such persons.-History:In...
, vagabond
Vagabond (person)
A vagabond is a drifter and an itinerant wanderer who roams wherever they please, following the whim of the moment. Vagabonds may lack residence, a job, and even citizenship....
, and vague come from the same root). Sometimes the branches are spoken of in the plural and are thus called vagi (ˈ). The vagus is also called the pneumogastric nerve since it innervates both the lungs and the stomach.
The motor division of the vagus nerve is derived from the basal plate
Basal plate (neural tube)
In the developing nervous system, the basal plate is the region of the neural tube ventral to the sulcus limitans. It extends from the rostral mesencephalon to the end of the spinal cord and contains primarily motor neurons, whereas neurons found in the alar plate are primarily associated with...
of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
, while the sensory division originates from the cranial neural crest
Cranial neural crest
The cranial neural crest is a form of neural crest.The cranial neural crest arises in the anterior and populates the face and the pharyngeal arches giving rise to bones, cartilage, nerves and connective tissue...
.
The vagus nerve includes axons which emerge from or converge onto three nuclei of the medulla:
- The Dorsal nucleus of vagus nerve - which sends parasympathetic output to the viscera esp intestines
- The Nucleus ambiguusNucleus ambiguusThe 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...
- which which sends parasympathetic output to the heart (slowing it down) and - The Solitary nucleusSolitary nucleusThe solitary tract and nucleus are structures in the brainstem that carry and receive visceral sensation and taste from the facial , glossopharyngeal and vagus cranial nerves.-Anatomy:...
- which receives afferent taste information and primary afferents from visceral organs
Branches
- Auricular nerve
- Pharyngeal nervePharyngeal branch of vagus nerveThe pharyngeal branch of the vagus nerve, the principal motor nerve of the pharynx, arises from the upper part of the ganglion nodosum, and consists principally of filaments from the cranial portion of the accessory nerve....
- Superior laryngeal nerveSuperior laryngeal nerveThe superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the ganglion nodosum and in its course receives a branch from the superior cervical ganglion of the sympathetic....
- Superior cervical cardiac branches of vagus nerveSuperior cervical cardiac branches of vagus nerveThe Superior Cardiac Branches , two or three in number, arise from the vagus, at the upper and lower parts of the neck....
- Inferior cervical cardiac branch
- Recurrent laryngeal nerveRecurrent laryngeal nerveThe recurrent laryngeal nerve is a branch of the vagus nerve that supplies motor function and sensation to the larynx . It travels within the endoneurium...
- Thoracic cardiac branches
- Branches to the pulmonary plexusPulmonary plexusThe pulmonary plexus is an autonomic plexus formed from pulmonary branches of vagus nerve and the sympathetic trunk.It supplies the Bronchial tree and the visceral pleura....
- Branches to the esophageal plexusEsophageal plexusThe 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...
- Anterior vagal trunkAnterior vagal trunkThe anterior vagal trunk is a branch of the vagus nerve which contributes to the esophageal plexus. It consists primarily of fibers from the left vagus, but also contains a few fibers from the right vagus.-External links:...
- Posterior vagal trunkPosterior vagal trunkThe posterior vagal trunk is a branch of the vagus nerve which contributes to the esophageal plexus. It consists primarily of fibers from the right vagus, but also contains a few fibers from the left vagus.-External links:...
- Hering-Breuer reflexHering-Breuer reflexThe Hering–Breuer inflation reflex, named for Josef Breuer and Ewald Hering, is a reflex triggered to prevent over-inflation of the lungs. Pulmonary stretch receptors present in the smooth muscle of the airways respond to excessive stretching of the lung during large inspirations.Once activated,...
in alveoli
The vagus runs posterior to the common carotid artery and internal jugular vein inside the carotid sheath.
Innervation
Right and left vagus nerves descend from the cranial vault through the jugular foramena, penetrating the carotid sheathCarotid sheath
The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the vascular compartment of the neck. It is part of the deep cervical fascia of the neck, below the superficial cervical fascia meaning the subcutaneous adipose tissue immediately beneath the skin.The deep...
between the internal and external carotid arteries, then passing posterolateral to the common carotid artery. The cell bodies of visceral afferent
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...
fibers of the vagus nerve are located bilaterally in the inferior ganglion of the vagus nerve (nodose ganglia).
The right vagus nerve gives rise to the right recurrent laryngeal nerve, which hooks around the right subclavian artery and ascends into the neck between the trachea and esophagus. The right vagus then crosses anteriorly to the right subclavian artery and runs posterior to the superior vena cava and descends posterior to the right main bronchus and contributes to cardiac, pulmonary, and esophageal plexuses. It forms the posterior vagal trunk at the lower part of the esophagus and enters the diaphragm through the esophageal hiatus.
The left vagus nerve enters the thorax between left common carotid artery and left subclavian artery and descends on the aortic arch. It gives rise to the left recurrent laryngeal nerve, which hooks around the aortic arch to the left of the ligamentum arteriosum and ascends between the trachea and esophagus. The left vagus further gives off thoracic cardiac branches, breaks up into pulmonary plexus, continues into the esophageal plexus, and enters the abdomen as the anterior vagal trunk in the esophageal hiatus of the diaphragm.
The vagus nerve supplies motor parasympathetic fibers to all the organs except the suprarenal (adrenal) glands, from the neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
down to the second segment of the transverse colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
. The vagus also controls a few skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
s, notable ones being:
- Cricothyroid muscleCricothyroid muscleThe cricothyroid muscle is the only tensor muscle of the larynx, aiding with phonation. It attaches to the anterolateral aspect of the cricoid and the inferior cornu and lower lamina of the thyroid cartilage, and its action tilts the thyroid forward to help tense the vocal cords...
- Levator veli palatini muscle
- Salpingopharyngeus muscleSalpingopharyngeus muscleThe salpingopharyngeus muscle arises from the inferior part of the cartilage of the pharyngotympanic tube in the nasal cavity; it passes downward and blends with the posterior fasciculus of the palatopharyngeus muscle....
- Palatoglossus musclePalatoglossus muscleThe palatoglossus, glossopalatinus, or palatoglossal muscle is a small fleshy fasciculus, narrower in the middle than at either end, forming, with the mucous membrane covering its surface, the glossopalatine arch....
- Palatopharyngeus musclePalatopharyngeus muscleThe palatopharyngeus or palatopharyngeal or pharyngopalatinus muscle is a long, fleshy fasciculus, narrower in the middle than at either end, forming, with the mucous membrane covering its surface, the palatopharyngeal arch.-Origin and insertion:...
- Superior, middle and inferior pharyngeal constrictorPharyngeal constrictorPharyngeal constrictor refers to one of the muscles that serves to constrict the pharynx.They include:* Superior pharyngeal constrictor muscle* Middle pharyngeal constrictor muscle* Inferior pharyngeal constrictor muscle...
s - Muscles of the larynxLarynxThe larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
(speech).
This means that the vagus nerve is responsible for such varied tasks as heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
, gastrointestinal peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
, sweating
Sweating
Perspiration is the production of a fluid consisting primarily of water as well as various dissolved solids , that is excreted by the sweat glands in the skin of mammals...
, and quite a few muscle movements in the mouth, including speech (via the recurrent laryngeal nerve
Recurrent laryngeal nerve
The recurrent laryngeal nerve is a branch of the vagus nerve that supplies motor function and sensation to the larynx . It travels within the endoneurium...
) and keeping the larynx open for breathing (via action of the posterior cricoarytenoid muscle
Posterior cricoarytenoid muscle
The posterior cricoarytenoid muscles are extremely small, paired muscles that extend from the posterior cricoid cartilage to the arytenoid cartilages in the larynx. By rotating the arytenoid cartilages laterally, these muscles abduct the vocal cords and thereby open the rima glottidis. Their action...
, the only abductor of the vocal folds). It also has some afferent fibers that innervate the inner (canal) portion of the outer ear
Outer ear
The outer ear is the external portion of the ear, which consists of the pinna, concha, and external auditory meatus. It gathers sound energy and focuses it on the eardrum . One consequence of the configuration of the external ear is to selectively boost the sound pressure 30- to 100-fold for...
, via the Auricular branch (also known as Alderman's nerve
Alderman's nerve
The auricular branch of the vagus nerve is often termed the Alderman's nerve or Arnold's nerve. The latter name is an eponym for Friedrich Arnold.-Path:...
) and part of the meninges
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
. This explains why a person may cough when tickled on the ear (such as when trying to remove ear wax with a cotton swab).
The vagus nerve and the heart
Parasympathetic innervation of the heartHeart
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...
is controlled by the vagus nerve. To be specific, the vagus nerve acts to lower the heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
. The right vagus innervates the sinoatrial node. Parasympathetic hyperstimulation predisposes those affected to bradyarrhythmias. The left vagus when hyperstimulated predisposes the heart to atrioventricular (AV) blocks
Heart block
A heart block can be a blockage at any level of the electrical conduction system of the heart .* Blocks that occur within the sinoatrial node are described as SA nodal blocks....
.
At this location, neuroscientist Otto Loewi
Otto Loewi
Otto Loewi was a German born pharmacologist whose discovery of acetylcholine helped enhance medical therapy. The discovery earned for him the Nobel Prize in Physiology or Medicine in 1936 which he shared with Sir Henry Dale, whom he met in 1902 when spending some months in Ernest Starling's...
first proved that nerves secrete substances called neurotransmitters, which have effects on receptors in target tissues. In his experiment, Loewi electrically stimulated the vagus nerve of a frog heart, which slowed the heart. Then he took the fluid from the heart and transferred it to a second frog heart without a vagus nerve. The second heart slowed down without an electrical stimulation. Loewi described the substance released by the vagus nerve as vagusstoff
Vagusstoff
Vagusstoff refers to the substance released by stimulation of the vagus nerve which causes a reduction in the heart rate. Discovered in 1921 by physiologist Otto Loewi, vagusstoff was the first confirmation of chemical synaptic transmission and the first neurotransmitter ever discovered...
, which was later found to be acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
.
Drugs that inhibit the muscarinic cholinergic receptor (anticholinergics) such as atropine
Atropine
Atropine is a naturally occurring tropane alkaloid extracted from deadly nightshade , Jimson weed , mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a drug with a wide variety of effects...
and scopolamine
Scopolamine
Scopolamine, also known as levo-duboisine, and hyoscine, is a tropane alkaloid drug with muscarinic antagonist effects. It is among the secondary metabolites of plants from Solanaceae family of plants, such as henbane, jimson weed and Angel's Trumpets , and corkwood...
are called vagolytic because they inhibit the action of the vagus nerve on the heart, gastrointestinal tract, and other organs. Anticholinergic drugs increase heart rate and are used to treat bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
(slow heart rate) and asystole
Asystole
In medicine, asystole is a state of no cardiac electrical activity, hence no contractions of the myocardium and no cardiac output or blood flow...
, which is when the heart has no electrical activity.
Medical treatment involving the vagus nerve
Vagus nerve stimulationVagus nerve stimulation
Vagus nerve stimulation is an adjunctive treatment for certain types of intractable epilepsy and treatment-resistant depression.- Mechanism of action :...
(VNS) therapy using a pacemaker-like device implanted in the chest is a treatment used since 1997 to control seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s in epilepsy patients and has recently been approved for treating drug-resistant cases of clinical depression
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
. A non-invasive VNS device that stimulates an afferent branch of the vagus nerve is also being developed and will soon undergo trials.
Clinical trials are currently underway in Antwerp, Belgium using VNS for the treatment of tonal tinnitus
Tinnitus
Tinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...
after a breakthrough study published in early 2011 by researchers at the University of Texas - Dallas showed successful tinnitus
Tinnitus
Tinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...
suppression in rats when tones were paired with brief pulses of stimulation of the vagus nerve.
http://www.utdallas.edu/news/2011/1/13-8021_Findings-Show-Promise-in-Battle-Against-Tinnitus_article.html
VNS may also be achieved by one of the vagal maneuvers: holding the breath for a few seconds, dipping the face in cold water, coughing, or tensing the stomach muscles as if to bear down to have a bowel movement. Patients with supraventricular tachycardia
Supraventricular tachycardia
Supraventricular tachycardia is a general term that refers to any rapid heart rhythm originating above the ventricular tissue. Supraventricular tachycardias can be contrasted to the potentially more dangerous ventricular tachycardias - rapid rhythms that originate within the ventricular...
, atrial fibrillation
Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
, and other illnesses may be trained to perform vagal maneuvers (or find one or more on their own).
Vagus nerve blocking (VBLOC) therapy is similar to VNS but used only during the day. In a six-month open-label trial
Open-label trial
An open-label trial or open trial is a type of clinical trial in which both the researchers and participants know which treatment is being administered....
involving three medical centers in Australia, Mexico, and Norway, vagus nerve blocking has helped 31 obese participants lose an average of nearly 15 percent of their excess weight. A year-long 300-participant double-blind, phase II trial has begun.
Vagotomy
Vagotomy
A vagotomy is a surgical procedure that involves resection of the vagus nerve.-Applications:Truncal vagotomy is a treatment option for chronic duodenal ulcers...
(cutting of the vagus nerve) is a now-obsolete therapy that was performed for peptic ulcer disease. Vagotomy is currently being researched as a less invasive alternative weight-loss procedure to gastric bypass surgery
Gastric bypass surgery
Gastric bypass procedures are any of a group of similar operations that first divides the stomach into a small upper pouch and a much larger lower "remnant" pouch and then re-arranges the small intestine to allow both pouches to stay connected to it. Surgeons have developed several different ways...
. The procedure curbs the feeling of hunger and is sometimes performed in conjunction with putting bands on patients' stomachs, resulting in average weight loss of 43% at six months with diet and exercise.
One serious side-effect of a Vagotomy is a Vitamin B-12 deficiency later in life - i.e., 10 years - that is similar to pernicious anemia. As one gets older, the stomach produces less acid. The acid, and one of its components called Intrinsic Factor
Intrinsic factor
Intrinsic factor also known as gastric intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the small intestine...
, is needed to metabolize B-12 from food. The vagotomy reduces the acid that ultimately leads to the deficiency, which, if left untreated, causes nerve damage, tiredness, dementia, paranoia, and ultimately death.
Physical and emotional effects
Activation of the vagus nerve typically leads to a reduction in heart rate, blood pressure, or both. This occurs commonly in the setting of gastrointestinal illness such as viral gastroenteritis or acute cholecystitis, or in response to other stimuli, including carotid sinusCarotid sinus
In human anatomy, the carotid sinus is a localized dilation of the internal carotid artery at its origin, the common carotid artery.-Functions:...
massage, Valsalva maneuver
Valsalva maneuver
The Valsalva maneuver or Valsalva manoeuvre is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...
, or 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."...
from any cause, in particular, having blood drawn. When the circulatory changes are great enough, vasovagal syncope
Vasovagal syncope
A vasovagal episode or vasovagal response or vasovagal attack is a malaise mediated by the vagus nerve. When it leads to syncope or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.There are a number of different syncope syndromes which all fall under the...
results. Relative dehydration tends to amplify these responses.
Excessive activation of the vagal nerve during emotional stress, which is a parasympathetic overcompensation of a strong sympathetic nervous system response associated with stress, can also cause vasovagal syncope
Vasovagal syncope
A vasovagal episode or vasovagal response or vasovagal attack is a malaise mediated by the vagus nerve. When it leads to syncope or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.There are a number of different syncope syndromes which all fall under the...
because of a sudden drop in blood pressure and heart rate. Vasovagal syncope affects young children and women more than other groups. It can also lead to temporary loss of bladder control under moments of extreme fear.
Research has shown that women having had complete spinal cord injury
Spinal cord injury
A spinal cord injury refers to any injury to the spinal cord that is caused by trauma instead of disease. Depending on where the spinal cord and nerve roots are damaged, the symptoms can vary widely, from pain to paralysis to incontinence...
can experience orgasm
Orgasm
Orgasm is the peak of the plateau phase of the sexual response cycle, characterized by an intense sensation of pleasure...
s through the vagus nerve, which can go from the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, cervix
Cervix
The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall...
, and, it is presumed, the vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
to the brain.
Liver - Insulin signaling activates the adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in the Arcuate nucleus
Arcuate nucleus
The arcuate nucleus is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence...
, decreases AgRP release, and through the vagus nerve, leads to decreased glucose production by the liver by decreasing gluconeogenic enzymes : Phosphoenolpyruvate carboxykinase
Phosphoenolpyruvate carboxykinase
Phosphoenolpyruvate carboxykinase is an enzyme in the lyase family used in the metabolic pathway of gluconeogenesis. It converts oxaloacetate into phosphoenolpyruvate and carbon dioxide.It is found in two forms, cytosolic and mitochondrial....
, Glucose 6-phosphatase
Glucose 6-phosphatase
Glucose 6-phosphatase is an enzyme that hydrolyzes glucose-6-phosphate resulting in the creation of a phosphate group and free glucose. Glucose is then exported from the cell via glucose transporter membrane proteins...
)
Effects of vagus nerve lesions
The patient complains of hoarse voice, difficulty in swallowing (dysphagiaDysphagia
Dysphagia is the medical term for the symptom of difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, the term is sometimes used as a condition in its own right. Sufferers are sometimes unaware of their dysphagia....
), and choking when drinking fluid. There is also loss of gag reflex. Uvula
Uvula
The palatine uvula, usually referred to as simply the uvula , is the conic projection from the posterior edge of the middle of the soft palate, composed of connective tissue containing a number of racemose glands, and some muscular fibers .-Function in language:The uvula plays a role in the...
deviates away from the side of lesion, and there is failure of palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
elevation.
See also
- PorphyriaPorphyriaPorphyrias are a group of inherited or acquired disorders of certain enzymes in the heme bio-synthetic pathway . They are broadly classified as acute porphyrias and cutaneous porphyrias, based on the site of the overproduction and accumulation of the porphyrins...
— This rare disorder can cause seizures and damage to the vagal nerve. Diagnosis, in some cases, may require DNA testing. - Vagovagal reflexVagovagal reflexVagovagal reflex refers to gastrointestinal tract reflex circuits where afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain. The vagovagal reflex controls contraction of the gastrointestinal muscle layers in response to...
- Vagus nerve stimulationVagus nerve stimulationVagus nerve stimulation is an adjunctive treatment for certain types of intractable epilepsy and treatment-resistant depression.- Mechanism of action :...