VAGUS NERVE

 

ORIGIN: Floor of the 4th ventricle in the upper medulla.

COURSE/DISTRIBUTION: This is the longest nerve in the human body extending from the medulla to the junction between the distal 1/3 and proximal 2/3 of the transverse colon. It starts its extrabulbar journey as rootlets, which pass in the interval between the olive and the inferior cerebellar peduncle, below the rootlets of the glossopharyngeal nerve and behind those of the hypoglossal nerve. The rootlets join together to form single nerve, which traverses the jugular foramen. It enters the foramen below the glossopharyngeal nerve and above the accessory nerve. It enters with the accessory nerve, the transverse slit of the middle compartment of that foramen where it lies medial to the accessory nerve before it perforates the arachnoid and dura mater, to become extracranial. Its extracranial course differs from the right and left nerves. But its ganglia are placed just below the jugular foramen and they are two.

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A small superior ganglion (also called jugular ganglion), which contains cell bodies for the relatively unimportant somatic fibers coming from the meningeal and auricular peripheral fibers.

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A large inferior ganglion called the ganglion nodosum, which has cell bodies for pseudounipolar sensory neurons associated with the vagus. They include fibers which mediate taste from the epiglottis, and fibers for general sensation in the epiglottal, hypopharyngeal, and other thoracic viscera.

At the formation of the inferior ganglion, the cranial accessory nerve gives its contained nucleus ambiguus fibers to the vagus nerve, which then distributes them to the recurrent laryngeal nerve.

Neck

The vagus nerve continues its journey on both sides in the carotid sheath lying on the side of the internal carotid artery, between the artery and the internal jugular vein  and later on the common carotid artery. It ends at the root of the neck where it passes in front of the subclavian artery in order to enter the mediastinum. Its cervical (neck) braches are numerous (see below).

Thorax

In the thorax, the vagus nerve descends in front of the subclavian artery to enter the thorax. Each vagus nerve (right or left) is attempting to reach the midline as it courses down the mediastinum. The left vagus crosses in front of the arch of the aorta deep to the left superior intercostal vein, as it gives off its recurrent laryngeal nerve, which hooks around the ligamentum arteriosum. It then passes behind the root of the left lung to reach the midline and form the esophageal plexus around the esophagus in the posterior mediastinum. It gives a large contribution to the pulmonary plexus as it passes behind the root of the lung.

The right vagus nerve is initially in contact with the trachea. It then passes behind the right lung root and gives its pulmonary branch to the pulmonary plexus around the root. It reaches the esophageal plexus around the esophagus where the left and the right vagi mix to produce two vagal trunks,

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Anterior vagal trunk (left vagus)

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Posterior vagal trunk (right vagus).

Abdomen

The anterior vagal trunk enters the abdomen via the esophageal opening at the level of T10, in front of the esophagus. It then gives a cardiac branch to the cardia of the stomach before dividing into three terminal branches. The posterior vagus also enters the abdomen via the esophageal opening, behind the esophagus. It ends in the celiac plexus where its branches reach the whole of the alimentary tract up to the junction between the distal 1/3 and proximal 2/3 of transverse colon.

BRANCHES:

Cervical:

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Meningeal

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Auricular

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Pharyngeal

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Carotid body nerve

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Superior laryngeal nerve

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Right recurrent laryngeal nerve

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Cervical cardiac

Thoracic:

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Thoracic cardiac

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Left recurrent laryngeal nerve

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Pulmonary

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Esophageal

Abdominal

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Anterior

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Posterior

FIBER TYPES:

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GSA fibers are pseudounipolar neurons whose peripheral fibers connect with auricular and meningeal nerves, which have somatic sensory nerves

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GVA fibers are pseudounipolar neurons for general sensation in the carotid body and in the thoracic viscera, such as the lungs, trachea and esophagus. The carotid body is  provided with end receptors such as baroreceptors and chemoreceptors. General sensation of the rest of the vagal area (abdomen) is from the sympathetic nerves

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GVE parasympathetic fibers, which arise from the caudal aspect of the inferior  salivatory nucleus in the floor of the 4th ventricle at the vagal trigone of the upper medulla. These fibers are for secretomotor functions in the areas supplied by the vagus nerve- e.g. secretion of hydrochloric acid in the stomach or enzymes in the whole of the gastrointestinal tract up to the transverse colon.  But other GVE fibers are associated with smooth muscle function. They assist the contraction of smooth muscles in the alimentary tract and the bronchial tree. They also assist the contraction of the heart and their nucleus is in the dorsal nucleus of vagus at the vagal trigone.

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SVE fibers are from the nucleus ambiguus. They supply the muscles of the 4th and 6th arches as follows- intrinsic muscles of the pharynx and those of the larynx (excluding the cricothyroid).

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SVA fibers, which mediate taste from the epiglottis. Their cell bodies lie in the nodosal ganglion and the central processes relay in the nucleus of the tractus solitarius in the pons.

ROOT:

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Motor fibers have two roots- dorsal nucleus of vagus and the inferior salivatory nucleus - all in the vagal trigone of the rhomboid fossa. Also motor fibers for the muscles derived from the 4th and 6th arches are from the caudal extreme of nucleus ambiguus.

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Sensory fibers are from the nucleus of spinal tract of V (auricular and meningeal), nucleus of tractus solitarius (taste for epiglottis) and general sensation (for thoracic viscera and the carotid body) all associated with the floor of 4th ventricle in the vagal trigone.

 

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Creator: Oluwole Ogunranti


 

 



 

 

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