Carotid sheath:Vagus

The **vagus nerve** is the tenth cranial nerve and provides the bulk of the parasympathetic input to the gastrointestinal system and to the heart. It is a mixed sensory/motor/parasympathetic nerve.

The vagus nerve arises as multiple rootlets at the posterolateral sulcus of the medulla, between the inferior cerebellar peduncle and olivary nucleus.

Origin:

Vagal nuclei are in upper and middle medulla

* Motor fibers originate in nucleus ambiguus
* Taste from epiglottis goes to solitary tract nucleus
* Sensory fibers from viscera terminate in dorsal vagal nucleus (afferent component)
* Parasympathetic fibers project from dorsal vagal nucleus (efferent component)
* Sensory from regional meninges and ear project to spinal nucleus CN5

Intra-Axial Segment

* Fibers to and from these nuclei exit lateral medulla in postolivary sulcus inferior to CN9 and superior to bulbar portion of CN11

Cisternal Segment

* Exits lateral medulla in postolivary sulcus and travel anterolaterally through premedullary cistern with CN9 and bulbar portion of CN11

Skull Base Segment

* Passes through posterior pars vascularis portion of jugular foramen (JF)
	+ Accompanied by CN11 and jugular bulb
	+ Superior vagal ganglion is found within jugular foramen and the inferior (nodose) ganglion lies approximately 1cm distally

Extracranial Segment

* Exits jugular fossa into the carotid space and descends vertically through the neck within the carotid sheath, where it lies posteriorly between the internal/common carotid artery and internal jugular vein.
* At the root of the neck, it is medial to the anterior scalene (while the phrenic nerve is anterior), posterior to the subclavian vein and anterior to the subclavian artery

* The **left vagus nerve** descend away from the trachea due to greater arteries. It crosses anterior to the aorta arch and posterior to the hilum of the left lung, towards the oesophageal hiatus. At the inferior border of the arch, it gives off the left recurrent branch.

* The **right vagus nerve** descends in the tracheo-oesophageal groove. It reaches the right paratracheal region posterior to the lung hilum. It passes through to the diaphragm as the posterior vagal trunk. At the root of the neck, it gives off the right recurrent branch around the right subclavian artery.
* Around the oesophageal hiatus the **left and right vagus nerves** meet and join to form the oesophageal plexus, from which gastric nerves emerge and and descend into the abdomen to provide parasympathetic innervation to stomach
* Innervation to intestines and visceral organs follows arterial blood supply to that organ

Branches

The branches of the vagus nerve from proximal to distal.

From the **superior ganglion**:

* small meningeal nerve: pass up to supply the dura mater of the posterior fossa below tentorium
* auricular nerve (Arnold's nerve): runs laterally through a small canal in the wall of the jugular fossa and supplies tympanic membranes and small area of external meatus.
* small communicating branches

From the **inferior ganglion**:

* *pharyngeal nerve to the pharyngeal plexus:* pass forward between internal and external carotid and joins pharyngeal plexus on the middle constrictor muscle, supply epiglottis, motor to pharyngeal muscles and soft palate (except stylopharyngeus and tensor palati), trachea and oesophagus.
* carotid body branches
* *superior laryngeal nerve:* slopes downwards on the side wall of the pharynx deep to internal carotid artery. Divides into large internal laryngeal nerve and pierce the thyrohyoid membrane for sensory supply of supraglottis, and into external laryngeal nerve that run close to superior thyroid vessels to supply cricothyroid.

From the **vagus nerve**:

* *recurrent laryngeal nerve:* hooks around **right subclavian** on right and **ligamentum arteriosum** on left, and ascend along posterolateral border of the trachea. Each nerve is under the pretracheal fascia. The nerve runs behind the cricothyroid joint and pass under the lower border of the inferior constrictor and at the level of the isthmus, divide into anterior and posterior branch. Supply motor to all laryngeal muscles except cricothyroids and sensory to mucosa of infraglottis
* superior and inferior cardiac nerves
* anterior and posterior bronchial nerves
* oesophageal plexus
	+ gastric nerves
* *coeliac plexus:* from the right vagus
* *hepatic plexus:* from the left vagus