CN X: Vagus nerve

CN X: Vagus nerveAnatomy and function of the vagus nerve
~ 10 min

In this note, we are going to discuss the anatomy and function of the vagus nerve (n. vagus), which is the CN X.

Vagus nerve (n. vagus)
Vagus nerve (n. vagus)

This nerve carries out several functions.

According to the generally accepted classification of functional components, it contains the following fiber types:

  • general somatic afferent fibers (GSA)
  • general visceral afferent fibers (GVA)
  • special visceral afferent fibers (SVA)
  • general visceral efferent fibers (GVE)
  • special visceral efferent (SVE) or branchiomotor fibers

Therefore, the vagus nerve is a mixed nerve.

Nuclei of the vagus nerve

The nucleus ambiguus (nucl. ambiguus), which is located in the dorsal part of the medulla posteriorly to the inferior olivary nucleus, is the source of the motor fibers.

Nucleus ambiguus (nucleus ambiguus)
Nucleus ambiguus (nucleus ambiguus)
Nucleus ambiguus (nucleus ambiguus)
Nucleus ambiguus (nucleus ambiguus)

The sensory fibers are formed by the processes of the pseudounipolar neurons of the superior ganglion

Superior ganglion (ganglion superius)
Superior ganglion (ganglion superius)

and inferior ganglion, which are located in the region of the jugular foramen.

Inferior ganglion (ganglion inferius)
Inferior ganglion (ganglion inferius)

The central processes of the sensory neurons synapse with the neurons of the solitary nucleus (nucl. tractus solitarii), as well as the spinal nucleus of the trigeminal nerve (nucleus spinalis nervi trigemini).

Solitary nucleus (nucleus solitarius / nucleus tractus solitarii)
Solitary nucleus (nucleus solitarius / nucleus tractus solitarii)
Solitary nucleus (nucleus solitarius / nucleus tractus solitarii)
Solitary nucleus (nucleus solitarius / nucleus tractus solitarii)

The solitary nucleus receives fibers of general visceral and special visceral (i.e., gustatory) sensations.

Spinal nucleus of the trigeminal nerve (nucleus spinalis nervi trigemini)
Spinal nucleus of the trigeminal nerve (nucleus spinalis nervi trigemini)
Spinal nucleus of the trigeminal nerve (nucleus spinalis nervi trigemini)
Spinal nucleus of the trigeminal nerve (nucleus spinalis nervi trigemini)

And the spinal nucleus of the trigeminal nerve receives fibers of general somatic sensation.

The dorsal nucleus of the vagus nerve (nucl. dorsalis n. vagi) is located in the dorsal part of the medulla and projects onto the rhomboid fossa. It is the source of the preganglionic parasympathetic fibers.

Dorsal nucleus of the vagus nerve (nucleus dorsalis nervi vagi)
Dorsal nucleus of the vagus nerve (nucleus dorsalis nervi vagi)
Dorsal nucleus of the vagus nerve (nucleus dorsalis nervi vagi)
Dorsal nucleus of the vagus nerve (nucleus dorsalis nervi vagi)

The vagus nerve exits the brainstem in the form of 10–12 rootlets posteriorly to the olives, in the retroolivary groove (sulcus retroolivaris), inferiorly to the glossopharyngeal nerve.

Nerve exits the brain
Nerve exits the brain
Nerve exits the brain
Nerve exits the brain
Nerve exits the brain
Nerve exits the brain

The vagus nerve exits the cranium through the jugular foramen (foramen jugulare).

Jugular foramen (foramen jugulare)
Jugular foramen (foramen jugulare)
Nerve within the jugular foramen
Nerve within the jugular foramen

In the area of this foramen, the nerve forms two already mentioned enlargements — the superior ganglion (ganglion superius) and the inferior ganglion (ganglion inferius).

Superior ganglion (ganglion superius)
Superior ganglion (ganglion superius)
Inferior ganglion (ganglion inferius)
Inferior ganglion (ganglion inferius)

Slightly distal from the inferior ganglion, the vagus nerve courses along the cranial root of the accessory nerve (radix cranialis nervi accessorii).

Accessory nerve (n. accessorius)
Accessory nerve (n. accessorius)

The main branches and the innervation area of the vagus nerve are located within the jugular fossa, neck, thoracic and abdominal cavities.

Branches in the jugular fossa

In the head, in particular within the jugular fossa, this nerve gives off two motor branches formed by the peripheral processes of the sensory neurons of the superior ganglion:

1. The meningeal branch (r. meningeus), which arises at the superior ganglion and re-enters the skull via the jugular foramen. It innervates the dura mater of the posterior cranial fossa.

Meningeal branch (r. meningeus)
Meningeal branch (r. meningeus)

2. The auricular branch (r. auricularis), also referred to as Arnold’s nerve, which arises from the superior ganglion, courses through the mastoid canaliculus, then exits the petrous part of the temporal bone through the tympanomastoid fissure (fissura tympanomastoidea),

Auricular branch (r. auricularis)
Auricular branch (r. auricularis)
Mastoid canaliculus (canaliculus mastoideus)
Mastoid canaliculus (canaliculus mastoideus)
Tympanomastoid fissure (fissura tympanomastoidea)
Tympanomastoid fissure (fissura tympanomastoidea)

and innervates the external tympanic membrane and a portion of the posterior aspect of the auricle.

Branches in the neck

In the neck, the vagus nerve joins the neurovascular bundle of this region, where it passes between the internal jugular vein and the internal carotid artery, which continues into the common carotid artery along the way. It gives off several mixed branches on the neck.

Course of the nerve in the neck region
Course of the nerve in the neck region
Course of the nerve in the neck region
Course of the nerve in the neck region

1. Pharyngeal branches (rr. pharyngei), which arise from the inferior ganglion and contain visceral sensory and motor fibers. The nerve passes anteriorly between the external and internal carotid arteries to the wall of the pharynx.

Pharyngeal branches (rr. pharyngei)
Pharyngeal branches (rr. pharyngei)

The motor fibers innervate all the pharyngeal muscles, except for the stylopharyngeus muscle (m. stylopharyngeus), and all the soft palate muscles, except for the tensor veli palatini muscle (m. tensor veli palatini).

Stylopharyngeus muscle (m. stylopharyngeus) - NOT innervated by the vagus nerve
Stylopharyngeus muscle (m. stylopharyngeus) - NOT innervated by the vagus nerve
Tensor veli palatini muscle (m. tensor veli palatini) - NOT innervated by the vagus nerve
Tensor veli palatini muscle (m. tensor veli palatini) - NOT innervated by the vagus nerve

The listed innervated muscles are derivatives of the 4th pharyngeal arch.

The sensory and autonomic fibers innervate the mucous membrane of the pharynx, forming the pharyngeal plexus (plexus pharyngeus) together with the pharyngeal branches of the glossopharyngeal nerve and sympathetic fibers.

Pharyngeal plexus (plexus pharyngeus)
Pharyngeal plexus (plexus pharyngeus)

2. The superior laryngeal nerve (n. laryngeus superior),

Superior laryngeal nerve (n. laryngeus superior)
Superior laryngeal nerve (n. laryngeus superior)
Superior laryngeal nerve (n. laryngeus superior)
Superior laryngeal nerve (n. laryngeus superior)

which passes between the external and internal carotid arteries. This nerve divides into motor (external) and sensory (internal) branches. The latter arises from the inferior ganglion of the vagus nerve. The thin external branch (r. externus), accompanied by the superior thyroid artery, descends posteriorly to the thyroid gland,

External branch (r. externus)
External branch (r. externus)

reaching the cricothyroid muscle (m. cricothyroideus), supplying it.

External branch (m. cricothyroideus)
External branch (m. cricothyroideus)

Together with the superior laryngeal artery, the internal branch (r. internus) perforates the thyrohyoid membrane and provides sensory innervation of the mucous membrane of the larynx superiorly to the vocal folds.

Internal branch (r. internus)
Internal branch (r. internus)

The listed innervated structures are derivatives of the 4th pharyngeal arch.

3. The superior cervical cardiac branches (rr. cardiaci cervicales superiors),

Superior cervical cardiac branches (rr. cardiaci cervicales superiores)
Superior cervical cardiac branches (rr. cardiaci cervicales superiores)

which descend into the thoracic cavity and participate in the formation of the cardiac plexus (plexus cardiacus).

Cardiac plexus (plexus cardiacus)
Cardiac plexus (plexus cardiacus)

4. The recurrent laryngeal nerve (n. laryngeus recurrens), which contains branchiomotor fibers. This branch arises from the trunk of the vagus nerve in the thoracic cavity, but then it returns to the neck, looping around the aortic arch (arcus aortae) inferiorly from the left, and the subclavian artery (arteria subclavia) from the right.

Recurrent laryngeal nerve (n. laryngeus recurrens)
Recurrent laryngeal nerve (n. laryngeus recurrens)

It passes into the groove between the trachea and the esophagus, innervating the initial part of each of these organs,

Recurrent laryngeal nerve (n. laryngeus recurrens)
Recurrent laryngeal nerve (n. laryngeus recurrens)

and gives off the inferior cervical cardiac branches (rr. cardiaci cervicales inferiores).

Inferior cervical cardiac branches (rr. cardiaci cervicales inferiores)
Inferior cervical cardiac branches (rr. cardiaci cervicales inferiores)

Behind the thyroid gland, the recurrent laryngeal nerve has a complex topographic and anatomical relationship with the inferior thyroid artery. The nerve may pass anteriorly or posteriorly to the artery, as well as between its branches.

Inferior thyroid artery (a. thyroidea inferior)
Inferior thyroid artery (a. thyroidea inferior)

Approaching the larynx, it is called the inferior laryngeal nerve (n. laryngeus inferior), which innervates all the muscles of this organ, except for the сricothyroid muscle, as well as its mucous membrane inferiorly to the vocal folds.

Inferior laryngeal nerve (n. laryngeus inferior)
Inferior laryngeal nerve (n. laryngeus inferior)

Branches in the thorax

Next, the vagus nerve descends into the thoracic cavity.

Here, the right vagus nerve passes anteriorly to the subclavian artery and posteriorly to the superior vena cava and the right main bronchus.

Vagus nerve (right) (n. vagus dexter)
Vagus nerve (right) (n. vagus dexter)

And the left vagus nerve passes between the left common carotid and subclavian arteries, descends along the aortic arch, and then posteriorly to the left main bronchus.

Vagus nerve (left) (n. vagus sinister)
Vagus nerve (left) (n. vagus sinister)

Within the thoracic cavity, the nerve gives off the bronchial branches (rr. bronchiales),

Bronchial branches (rr. bronchiales)
Bronchial branches (rr. bronchiales)

esophageal branches (rr. esophagei),

Esophageal branches (rr. esophagei)
Esophageal branches (rr. esophagei)

and thoracic cardiac branches (rr. cardiaci thoracici),

Thoracic cardiac branches (rr. cardiaci thoracici)
Thoracic cardiac branches (rr. cardiaci thoracici)

which form the pulmonary (plexus pulmonalis),

Pulmonary plexus (plexus pulmonalis)
Pulmonary plexus (plexus pulmonalis)

esophageal (plexus oesophageus),

Esophageal plexus (plexus oesophageus)
Esophageal plexus (plexus oesophageus)

and cardiac plexuses (plexus cardiacus), respectively.

Cardiac plexus (plexus cardiacus)
Cardiac plexus (plexus cardiacus)

Two vagal trunks: the anterior trunk (truncus vagalis anterior)

Anterior trunk (truncus vagalis anterior)
Anterior trunk (truncus vagalis anterior)
Anterior trunk (truncus vagalis anterior)
Anterior trunk (truncus vagalis anterior)

and the posterior trunk (truncus vagalis posterior),

Posterior trunk (truncus vagalis posterior)
Posterior trunk (truncus vagalis posterior)
Posterior trunk (truncus vagalis posterior)
Posterior trunk (truncus vagalis posterior)

are formed from the esophageal plexus. Both trunks descend along the anterior and posterior surfaces of the esophagus, respectively, and enter the abdominal cavity via the esophageal hiatus of the diaphragm (hiatus oesophageus).

Esophageal hiatus of the diaphragm (hiatus oesophageus)
Esophageal hiatus of the diaphragm (hiatus oesophageus)

The anterior trunk is formed primarily by the left vagus nerve, while the posterior trunk is formed by the fibers of the right vagus nerve. 

Branches in the abdomen

In the abdominal cavity, the anterior trunk divides into branches that innervate the anterior wall of the stomach (rr. gastrici anteriores)

Anterior gastric branches (rr. gastrici anteriores)
Anterior gastric branches (rr. gastrici anteriores)
Anterior gastric branches (rr. gastrici anteriores)
Anterior gastric branches (rr. gastrici anteriores)

and gives off a large hepatic branch (r. hepaticus).

Hepatic branch (r. hepaticus)
Hepatic branch (r. hepaticus)

The latter ascends to the porta hepatis, giving off a branch to the pylorus of the stomach. The posterior trunk divides into branches innervating the posterior wall of the stomach (rr. gastrici posteriores).

Posterior gastric branches (rr. gastrici posteriores)
Posterior gastric branches (rr. gastrici posteriores)

The coeliac branches (rr. coeliaci) of the posterior trunk pass to the coeliac and superior mesenteric plexuses together with the sympathetic nerves, innervating the pancreas, the small intestine, and the large intestine up to the sigmoid colon.

Coeliac branches (rr. coeliaci)
Coeliac branches (rr. coeliaci)

So, the branches of the vagus nerve join the autonomic plexuses of the abdominal cavity, providing parasympathetic and sensory innervation to the internal organs. The preganglionic fibers synapse with the neurons in the intramural ganglia located within the walls of the organs. Stimulation of the vagus nerve causes dilation of the bronchi, a decrease in heart rate, and an increase in peristaltic activity, and furthermore it activates the secretion of the gastrointestinal glands.

Dictionary

CN X: Vagus nerve

Peripheral nervous system
systema nervosum periphericum
Vagus nerve
n. vagus
Superior and inferior ganglia
ganglion superius et ganglion inferius
Nucleus of the solitary tract
nucleus solitarius
Nucleus ambiguus
nucleus ambiguus
Dorsal nucleus of the vagus nerve
nucleus dorsalis nervi vagi
Spinal nucleus of the trigeminal nerve
nucleus spinalis nervi trigemini
Retro-olivary groove
sulcus retroolivaris
Jugular foramen
foramen jugulare
Cranual root of the accessory nerve
radix cranialis nervi accessorii
Meningeal branch
r. meningeus
Auricular branch
r. auricularis
Mastoid canaliculus
canaliculus mastoideus
Tympanomastoid fissure
fissura tympanomastoidea
Pharyngeal branches
rr. pharyngei
Stylopharyngeus muscle
m. stylopharyngeus
Tensor veli palatini muscle
m. tensor veli palatini
Superior cervical cardiac branches
rr. cardiaci cervicales superiores
Superior laryngeal nerve
n. laryngeus superior
External branch
r. externus
Cricothyroideus muscle
m. cricothyroideus
Internal branch
r. internus
Cardiac plexus
plexus cardiacus
Arch of the aorta
arcus aortae
Subclavian artery
arteria subclavia
Recurrent laryngeal nerve
n. laryngeus recurrens
Pharyngeal plexus
plexus pharyngeus
External branch
ramus externus
Internal branch
ramus internus
Inferior laryngeal nerve
n. laryngeus inferior
Tracheal branches
rr. tracheales
Esophageal branches
rr. oesophagei
Inferior cervical cardiac branches
rr. cardiaci cervicales inferiores
Thoracic cardiac branches
rr. cardiaci thoracici
Bronchial branches
rr. bronchiales
Pulmonary plexus
plexus pulmonalis
Esophageal plexus
plexus oesophageus
Anterior vagal trunk
truncus vagalis anterior
Anterior gastric branches
rr. gastrici anteriores
Hepatic branches
rr. hepatici
Posterior vagal trunk
truncus vagalis posterior
Esophageal hiatus
hiatus oesophageus
Posterior gastric branches
rr. gastrici posteriores
Coeliac branches
rr. coeliaci
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