Inferior Ganglion of Vagus Nerve

Location

The inferior ganglion of the vagus nerve sits extracranially, below the jugular foramen. The inferior ganglion of the vagus nerve is one of two ganglia associated with the vagus nerve. It develops from epibranchial placodal cells and sends its axons to the nucleus of the solitary tract (Barlow, 2002).

Branches

The inferior ganglion of the vagus nerve is a swelling through which the vagus nerve runs. In addition to transmitting the fibers of the vagus nerve to and from the brainstem, several branches of the vagus nerve originate in the inferior ganglion.

The pharyngeal branches run from the inferior ganglion inferiorly, crossing between the external and internal carotid arteries to reach the upper posterior surface of the middle pharyngeal constrictor muscle. Here they fan out and join with fibers of the glossopharyngeal nerve and sympathetic fibers to innervate all pharyngeal muscles, except stylopharyngeus, all palate muscles, except tensor veli palatini, and the mucosa of the root of the tongue, epiglottis, and pharynx. Special sense taste fibers from the epiglottis travel via the pharyngeal branches. The pharyngeal branches can also contribute to the carotid branches.

The carotid branches of the vagus nerve originate from the pharyngeal branches of the vagus nerve as well as directly from the vagus nerve. These fibers join with the descending carotid sinus nerve and a plexus of fibers wrapped around the internal carotid artery as they head to the carotid bifurcation. The majority of fibers reaching the carotid body and sinus are glossopharyngeal fibers. Vagal carotid branches are highly variable, and it is unclear what functional role they may play. They are presumed to convey information from chemoreceptors but play a minor role in carotid body and sinus function (Shoja and Oyesiku, 2014).

The superior laryngeal nerve originates at or near the inferior ganglion of the vagus nerve. It runs inferiorly, posterior to the internal carotid artery and on the lateral side of the pharynx to the greater horn of the hyoid bone where it divides into external and internal branches. The superior laryngeal nerve is a mixed nerve conveying motor innervation to the cricothyroid and inferior pharyngeal constrictor muscles. It conveys parasympathetic, visceral sensory, and special sensory innervation to the epiglottis, laryngopharynx, and upper larynx.

There are also often two communications that run from the inferior ganglion. Fibers travel to the inferior ganglion of the vagus from the accessory nerve. These represent the cranial root of the accessory nerve and convey branchial motor fibers to the pharynx. Although these fibers exit the cranium with the accessory nerve, they originate in the nucleus ambiguus with vagal branchial motor neurons. Many consider them to be vagal nerve fibers that rejoin the vagus nerve at the inferior ganglion rather than accessory nerve fibers that move over to the vagus nerve (Shoja et al., 2014). Additionally, sympathetic fibers from the superior cervical ganglion of the sympathetic chain can cross over to the inferior ganglion.

Supplied Structures

The inferior ganglion of the vagus nerve transmits most of the fibers of the vagus nerve, and contains axons of sensory, motor, and parasympathetic nature. However, neurons whose cell bodies are found in the superior ganglion are general visceral afferent and special visceral afferent neurons.

General visceral afferent fibers convey sensation from the mucosa of the epiglottic region, laryngopharynx, and larynx, as well as all thoracic and most abdominal visceral tissues. Special visceral afferent fibers convey taste sensation from the epiglottis and root of the tongue.

Parasympathetic fibers targeting the gut tube, thoracic and abdominal viscera, heart, and lungs, as well as branchial motor vagal fibers targeting most of the muscles of the palate, pharynx, and larynx pass through the inferior ganglion to reach their targets but do not synapse here.

List of Clinical Correlates

—Gag reflex

—Hoarseness

—Cough reflex

—Sleep apnea

—Bradycardia

—Hypotension

—Vagal nerve stimulation

References

Barlow, L. A. (2002) Cranial Nerve Development: Placodal Neurons Ride the Crest. Current Biology, 12(5), R171-R173.

Shoja, M. M. & Oyesiku, N. M. (2014) Clinical anatomy of the cranial nerves. Clin Anat, 27(1), 2-3.

Shoja, M. M., Oyesiku, N. M., Shokouhi, G., Griessenauer, C. J., Chern, J. J., Rizk, E. B., Loukas, M., Miller, J. H. & Tubbs, R. S. (2014) A comprehensive review with potential significance during skull base and neck operations, Part II: Glossopharyngeal, vagus, accessory, and hypoglossal nerves and cervical spinal nerves 1–4. Clinical Anatomy, 27(1), 131-144.