In this note, we are going to discuss the anatomy and function of the vagus nerve (n. vagus), which is the CN X.
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.
The sensory fibers are formed by the processes of the pseudounipolar neurons of the superior ganglion
and inferior ganglion, which are located in the region of the jugular foramen.
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).
The solitary nucleus receives fibers of general visceral and special visceral (i.e., gustatory) sensations.
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.
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.
The vagus nerve exits the cranium through the jugular foramen (foramen jugulare).
In the area of this foramen, the nerve forms two already mentioned enlargements — the superior ganglion (ganglion superius) and the 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).
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.
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),
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.
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.
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).
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.
2. The 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,
reaching the cricothyroid muscle (m. cricothyroideus), supplying it.
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.
The listed innervated structures are derivatives of the 4th pharyngeal arch.
3. The superior cervical cardiac branches (rr. cardiaci cervicales superiors),
which descend into the thoracic cavity and participate in the formation of the 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.
It passes into the groove between the trachea and the esophagus, innervating the initial part of each of these organs,
and gives off the 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.
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.
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.
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.
Within the thoracic cavity, the nerve gives off the bronchial branches (rr. bronchiales),
esophageal branches (rr. esophagei),
and thoracic cardiac branches (rr. cardiaci thoracici),
which form the pulmonary (plexus pulmonalis),
esophageal (plexus oesophageus),
and cardiac plexuses (plexus cardiacus), respectively.
Two vagal trunks: the anterior trunk (truncus vagalis anterior)
and the 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).
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)
and gives off a large 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).
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.
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.
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