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The vagus nerve is the tenth cranial nerve (CN X). It has the longest course of all the cranial nerves as it extends from the head, the neck, the thorax, and the abdomen. The vagus nerve originates in the medulla oblongata and exits the skull via the jugular foramen. It bears two ganglia, the superior ganglia, and the inferior ganglia. The superior ganglia lie in the jugular foramen and the inferior ganglia lie near the base of the skull.
Structure and Function
The vagus nerve contains somatic and visceral afferent fibers, as well as general and special visceral efferent fibers.
It has three major nuclei:
- Main motor nucleus: nucleus ambiguus
- Parasympathetic nucleus: dorsal nucleus of vagus - it is both, a motor nucleus (visceromotor and secretomotor) and a sensory nucleus (viscerosensory)
- Sensory nucleus: nucleus of tractus solitarius (situated in the inferior ganglion on the vagus nerve) and nucleus of the spinal tract of trigeminal (afferent information enters the brainstem through the superior ganglion of the vagus nerves but ends here). See the table below.
Table 1. Components, function, central component, and cell bodies of the vagus nerve
|Components||Function||Central component||Cell bodies|
|Special Visceral Efferent||Swallowing and phonation||Nucleus ambiguus||Nucleus ambiguus|
|General Visceral Efferent||Involuntary muscle control (cardiac, pulmonary, esophageal)
Innervation to glands throughout the gastrointestinal tract
|Dorsal motor nucleus||Dorsal motor nucleus|
|Special Visceral Afferent||Sensations of taste from the tongue and epiglottis ||Nucleus tractus solitarius||Inferior ganglion|
|General Visceral Afferent||Sensations from the pharynx, larynx, trachea, esophagus, and the abdominal and thoracic viscera||Nucleus tractus solitarius||Inferior ganglion|
|General Somatic Afferent||Innervation to the external ear and tympanic membrane||Nucleus of the spinal tract of trigeminal||Superior ganglion|
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. 
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. 
In the jugular foramen
- arises at the superior ganglion and re-enters the skull at the jugular foramen
- supplies the dura of the posterior cranial fossa
- also known as Arnold's nerve
- arises from the superior ganglion and re-enters the lateral portion of the jugular foramen via the mastoid canaliculus
- exits through the tympanomastoid suture of the temporal bone to reach and supply the skin
- innervates the external tympanic membrane and posterior half of external auditory meatus
In the neck
All the branches in the neck arise from the inferior ganglion and are as following:
- contains the fibers of the accessory nerve (CN XI)
- passes between the external and internal carotid arteries
- reaches the upper border of the middle pharyngeal constrictor muscle to form the pharyngeal plexus
- supply the pharyngeal muscles and soft palate except for the tensor palatini muscle
- passes between the external and internal carotid arteries at the level of hypoglossal nerve (CN XII)
- divides into internal and external branches at the hyoid
- The internal laryngeal nerve goes through the thyrohyoid membrane to enter the larynx; supplies the mucosa superior to the glottis
- The external laryngeal nerve travels distally with the superior thyroid vessels; supplies the cricothyroid muscle
Recurrent laryngeal nerve
- also known as the inferior laryngeal nerve
- Right recurrent laryngeal arises from the vagus in front of the right subclavian artery and travels superiorly to enter the larynx between the cricopharyngeus muscle and the esophagus
- Left recurrent laryngeal loops around the aortic arch distal to the ligamentum arteriosus and then enters the larynx
- supplies all the intrinsic muscles of the larynx, except the cricothyroid
Superior cardiac branches
- within the carotid sheath, it gives off the superior cardiac nerve
- associated with parasympathetic fibers and travels to the heart
- Anterior and posterior bronchial branches in which the anterior branches are along the anterior lung forming the anterior pulmonary plexus, whereas the posterior branches form the posterior pulmonary plexus.
- Esophageal branches of the vagus nerve are anterior and posterior and form the esophageal plexus 
- Gastric branches supply the stomach; celiac branches (mainly derived from the right vagus nerve) supply the pancreas, spleen, kidneys, adrenals, and small intestine
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.
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.
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.
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. 
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.
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. 
A paralyzed vagus nerve also produces:
- nasal regurgitation of swallowed liquid
- hypernasal speech
- flattening of the palatal arch
- uvula deviation
- cadaveric position of the vocal cord
Vagus nerve stimulation
- Berthoud HR, Neuhuber WL. Functional and chemical anatomy of the afferent vagal system. Autonomic Neuroscience. 2000 Dec 20;85(1-3):1-7.
- Kenny BJ, Bordoni B. Neuroanatomy, Cranial Nerve 10 (Vagus Nerve). InStatPearls [Internet] 2019 Jan 25. StatPearls Publishing.
- 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]
- 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]
- Garner DH, Baker S. Anatomy, Head and Neck, Carotid Sheath. InStatPearls [Internet] 2019 Feb 6. StatPearls Publishing.
- 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.
- Hammer N, Glätzner J, Feja C, Kühne C, Meixensberger J, Planitzer U, Schleifenbaum S, Tillmann BN, Winkler D. Human vagus nerve branching in the cervical region. PloS one. 2015 Feb 13;10(2):e0118006.
- Erman AB, Kejner AE, Hogikyan ND, Feldman EL. Disorders of cranial nerves IX and X. InSeminars in neurology 2009 Feb (Vol. 29, No. 1, p. 85). NIH Public Access.
- Fernando DA, Lord RS. The blood supply of vagus nerve in the human: its implication in carotid endarterectomy, thyroidectomy and carotid arch aneurectomy. Annals of Anatomy-Anatomischer Anzeiger. 1994 Aug 1;176(4):333-7.
- Dicpinigaitis PV, Kantar A, Enilari O, Paravati F. Prevalence of Arnold nerve reflex in adults and children with chronic cough. Chest. 2018 Mar 1;153(3):675-9.
- Montoya S, Portanova A, Bhatt AA. A radiologic review of hoarse voice from anatomic and neurologic perspectives. Insights into imaging. 2019 Dec;10(1):1-21.
- Hayward NJ, Grodski S, Yeung M, Johnson WR, Serpell J. Recurrent laryngeal nerve injury in thyroid surgery: a review. ANZ Journal of Surgery. 2013 Jan;83(1-2):15-21.