Vagus Nerve: Difference between revisions

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# The left vagus enters the thorax by passing between the left common carotid and left [[Vertebral Artery|subclavian]] arteries, then travels behind the primary left bronchus and into the esophagus.<ref name=":1" />
# The left vagus enters the thorax by passing between the left common carotid and left [[Vertebral Artery|subclavian]] arteries, then travels behind the primary left bronchus and into the esophagus.<ref name=":1" />


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== Parasympathetic Functions ==
== Clinical Significance ==
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The vagus nerve is commonly tested clinically by comparing the palatal arches on the two sides. A patient is often asked to open their mouth and say ‘ah,’ as this should cause elevation of the uvula. On the paralyzed side, there is no arching and the uvula is pulled to the normal side.
In the thorax and abdomen, the vagus nerve is the main parasympathetic outflow to the heart and gastro-intestinal organs.


As the vagus nerve and its branches supply many different structures in the body, a lesion along the course of the vagus nerve can cause different symptoms that may vary from palatal and pharyngeal paralysis to abnormalities in the gastric acid secretion and heart rate.  
'''The Heart''': Cardiac branches arise in the thorax, conveying parasympathetic innervation to the sino-atrial and atrio-ventricular nodes of the heart. These branches stimulate a reduction in the resting heart rate. They are constantly active, producing a rhythm of 60 – 80 beats per minute. If the vagus nerve was lesioned, the resting heart rate would be around 100 beats per minute.


Vasovagal syncope is one of the most common causes of fainting, which is due to the vagus nerve. For example, during a period of an unusual stimulus such as emotional stress, the body overreacts and causes the vagus nerve to a sudden drop in blood pressure and heart rate. A vasovagal syncope doesn't require a specific medical treatment but should be consulted to a physician if repeated episodes of syncope occur. Furthermore, a carotid massage may compress the carotid sinus leading to the perception of high blood pressure.
'''Gastro-Intestinal System''': The vagus nerve provides parasympathetic innervation to the majority of the abdominal organs. It sends branches to the oesophagus, stomach and most of the intestinal tract – up to the splenic flexure of the large colon. The function of the vagus nerve is to stimulate smooth muscle contraction and glandular secretions in these organs. For example, in the stomach, the vagus nerve increases the rate of gastric emptying, and stimulates acid production<ref>Teach me anatomy [https://teachmeanatomy.info/head/cranial-nerves/vagus-nerve-cn-x/ Vagus Nerve] Available from: https://teachmeanatomy.info/head/cranial-nerves/vagus-nerve-cn-x/<nowiki/>(accessed 31.1.2021)</ref>.<div class="row">
 
Unilateral damage to the pharyngeal branch may cause [[dysphagia]]. Lesions of the superior pharyngeal nerve results in paralysis of cricothyroid muscle and anesthesia in the upper part of the larynx. <ref name=":3">Erman AB, Kejner AE, Hogikyan ND, Feldman EL. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4239699/ Disorders of cranial nerves IX and X]. InSeminars in neurology 2009 Feb (Vol. 29, No. 1, p. 85). NIH Public Access.</ref>
 
Irritation of the auricular branch in the external ear may cause chronic cough (ear-cough reflex or Arnold's nerve ear-cough reflex). In children, enlarged lymph nodes may also irritate the recurrent laryngeal nerve and cause a persistent cough.<ref>Dicpinigaitis PV, Kantar A, Enilari O, Paravati F. [https://www.practiceupdate.com/content/prevalence-of-arnold-nerve-reflex-in-adults-and-children-with-chronic-cough/66394 Prevalence of Arnold nerve reflex in adults and children with chronic cough.] Chest. 2018 Mar 1;153(3):675-9.</ref>
 
An injury to the recurrent laryngeal nerve as a result of trauma, surgery, or a large tumor results in hoarseness and dysphonia due to the paralysis of the right vocal cord. <ref>Montoya S, Portanova A, Bhatt AA. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6861408/ A radiologic review of hoarse voice from anatomic and neurologic perspectives.] Insights into imaging. 2019 Dec;10(1):1-21.</ref>
 
Paralysis of both the vocal cords results in [[Lung Sounds|inspiratory stridor]] and aphonia and is very likely to occur in thyroid surgery.<ref>Hayward NJ, Grodski S, Yeung M, Johnson WR, Serpell J. [https://onlinelibrary.wiley.com/doi/full/10.1111/j.1445-2197.2012.06247.x Recurrent laryngeal nerve injury in thyroid surgery: a review.] ANZ Journal of Surgery. 2013 Jan;83(1-2):15-21.</ref>
 
A paralyzed vagus nerve also produces:
# nasal regurgitation of swallowed liquid
# hypernasal speech
# dysarthria
# flattening of the palatal arch
# uvula deviation
# cadaveric position of the vocal cord<ref name=":3" />  


== Resources  ==
== Resources  ==

Revision as of 08:14, 31 January 2021

Original Editor - Kanza Imtiaz

Top Contributors - Kanza Imtiaz, Lucinda hampton and Tony Lowe

This article is currently under review and may not be up to date. Please come back soon to see the finished work! (31/01/2021)

Introduction[edit | edit source]

Course and distribution of the glossopharyngeal, vagus, and accessory nerves..gif

The vagus nerve is the tenth cranial nerve (CN X) and is the longest mixed cranial nerve. The literal translation of the vagus is 'wanderer,' which aptly represents its widespread interfacing of cortex, brainstem, hypothalamus, and the body. Its afferent and efferent pathways comprise about 80% and 20%, respectively[1].

The vagus nerve runs from the brain through the face and thorax to the abdomen. It is a mixed nerve that contains parasympathetic fibres.

The vagus nerve has two sensory ganglia (masses of nerve tissue that transmit sensory impulses): the superior and the inferior ganglia.

  1. The branches of the superior ganglion innervate the skin in the concha of the ear.
  2. The inferior ganglion gives off two branches: the pharyngeal nerve and the superior laryngeal nerve.

The recurrent laryngeal nerve branches from the vagus in the lower neck and upper thorax to innervate the muscles of the larynx (voice box).

The vagus also gives off cardiac, esophageal, and pulmonary branches.

In the abdomen the vagus innervates the greater part of the digestive tract and other abdominal viscera[2].

The accessory nerve (CN XI) joins the vagus nerve just distal to the inferior ganglion.[3]

Structure and Function[edit | edit source]

The vagus nerve contains somatic and visceral afferent fibers, as well as general and special visceral efferent fibers.[4] See Table Below:

Components Function Central component Cell bodies
Special Visceral Efferent Swallowing and phonation[4] Nucleus ambiguus Nucleus ambiguus
General Visceral Efferent Involuntary muscle control (cardiac, pulmonary, esophageal)

Innervation to glands throughout the gastrointestinal tract[4]

Dorsal motor nucleus Dorsal motor nucleus
Special Visceral Afferent Sensations of taste from the tongue and epiglottis [4] Nucleus tractus solitarius Inferior ganglion
General Visceral Afferent Sensations from the pharynx, larynx, trachea, esophagus, and the abdominal and thoracic viscera[4] Nucleus tractus solitarius Inferior ganglion
General Somatic Afferent Innervation to the external ear and tympanic membrane[4] Nucleus of the spinal tract of trigeminal Superior ganglion
[5]
[6]

Course[edit | edit source]

Upper portions of glossopharyngeal, vagus, and accessory nerves
The Vagus nerve

Exits the brain from the medulla oblongata of the brainstem and travels laterally exiting the skull through the jugular foramen.

It descends within the carotid sheath where it is located posterolateral to the internal and common carotid arteries, and medial to the internal jugular vein.

At the base of the neck, the nerve enters the thorax, where the right and left vagus nerve travels on a different path. [7]

  1. The right vagus enters the thorax by crossing the first part of the subclavian artery and posterior to the innominate artery; then travels behind the primary right bronchus and esophagus to form the esophageal plexus with the left vagus nerve. [8]
  2. The left vagus enters the thorax by passing between the left common carotid and left subclavian arteries, then travels behind the primary left bronchus and into the esophagus.[8]

Parasympathetic Functions[edit | edit source]

In the thorax and abdomen, the vagus nerve is the main parasympathetic outflow to the heart and gastro-intestinal organs.

The Heart: Cardiac branches arise in the thorax, conveying parasympathetic innervation to the sino-atrial and atrio-ventricular nodes of the heart. These branches stimulate a reduction in the resting heart rate. They are constantly active, producing a rhythm of 60 – 80 beats per minute. If the vagus nerve was lesioned, the resting heart rate would be around 100 beats per minute.

Gastro-Intestinal System: The vagus nerve provides parasympathetic innervation to the majority of the abdominal organs. It sends branches to the oesophagus, stomach and most of the intestinal tract – up to the splenic flexure of the large colon. The function of the vagus nerve is to stimulate smooth muscle contraction and glandular secretions in these organs. For example, in the stomach, the vagus nerve increases the rate of gastric emptying, and stimulates acid production[9].

Resources[edit | edit source]

Vagus nerve stimulation

References[edit | edit source]

  1. ↑ Mandalaneni K, Rayi A. Vagus nerve stimulator. StatPearls [Internet]. 2020 Aug 20.Available from: https://www.ncbi.nlm.nih.gov/books/NBK562175/(accessed 31.1.2021)
  2. ↑ Britannica Vagus Nerve Available from: https://www.britannica.com/science/vagus-nerve (accessed 31.1.2021)
  3. ↑ Berthoud HR, Neuhuber WL. Functional and chemical anatomy of the afferent vagal system. Autonomic Neuroscience. 2000 Dec 20;85(1-3):1-7.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Kenny BJ, Bordoni B. Neuroanatomy, Cranial Nerve 10 (Vagus Nerve). InStatPearls [Internet] 2019 Jan 25. StatPearls Publishing.
  5. ↑ Kenhub - Learn Human Anatomy. Vagus nerve: location, branches and function (preview) - Neuroanatomy | Kenhub. Available from: https://www.youtube.com/watch?v=bNPfjLnnJzA [last accessed 23/9/2020]
  6. ↑ The Art of Living. What Is The Vagus Nerve? | Vagus Nerve Explained | Brain, Mind Body Connect. Available from: https://www.youtube.com/watch?v=gp67EQhNfj8 [last accessed 23/9/2020]
  7. ↑ Garner DH, Baker S. Anatomy, Head and Neck, Carotid Sheath. InStatPearls [Internet] 2019 Feb 6. StatPearls Publishing.
  8. ↑ 8.0 8.1 Yuan H, Silberstein SD. Vagus nerve and vagus nerve stimulation, a comprehensive review: part II. Headache: The Journal of Head and Face Pain. 2016 Feb;56(2):259-66.
  9. ↑ Teach me anatomy Vagus Nerve Available from: https://teachmeanatomy.info/head/cranial-nerves/vagus-nerve-cn-x/(accessed 31.1.2021)
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