Vagus Nerve

Original Editor - Kanza Imtiaz

Top Contributors - Kanza Imtiaz, Lucinda hampton and Tony Lowe

Introduction

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.

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

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:

1. Main motor nucleus: nucleus ambiguus
2. Parasympathetic nucleus: dorsal nucleus of vagus - it is both, a motor nucleus (visceromotor and secretomotor) and a sensory nucleus (viscerosensory)
3. 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. Summary of 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

Course

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.

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.

Branches

In the jugular foramen

Meningeal branch

• arises at the superior ganglion and re-enters the skull at the jugular foramen
• supplies the dura of the posterior cranial fossa

Auricular branch

• 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:

Pharyngeal branches

• 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

Superior laryngeal nerve

• 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
• 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

Other branches

1. 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.
2. esophageal branches of the vagus nerve are anterior and posterior and form the esophageal plexus
3. gastric branches supply the stomach; celiac branches (mainly derived from the right vagus nerve) supply the pancreas, spleen, kidneys, adrenals, and small intestine

Blood Supply

The middle meningeal artery supplies the intracranial blood supply to the vagus nerve. The extracranial blood supply comes from the common carotid artery, internal carotid artery, inferior thyroid artery, external carotid artery, a posterior meningeal artery, internal thoracic arteries, bronchial arteries, and esophageal arteries.

Clinical Significance

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,’ this should cause elevation of the uvula. There is no arching on the paralyzed side and the uvula is pulled to the normal side.

Paralysis of the vagus nerve causes:

1. nasal regurgitation of swallowed liquid
2. nasal twang voice
3. hoarseness of the voice

If, during the physical exam, the patient is noted to have hoarseness of the voice, this shows the need to test the vocal cords in the patient and if there is hoarseness with a normal gag reflex and palatal elevation, this indicates a lesion of the recurrent laryngeal nerve. Gag reflex should not be used as a clinical exam as there can be a bilateral loss of the gag reflex in a healthy patient too.

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