Glossopharyngeal nerve - Brain - Brainstem - e-Anatomy
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Glossopharyngeal nerve

Nervus glossopharyngeus

  • Latin synonym: Nervus cranialis IX
  • Synonym: Cranial nerve IX
  • Related terms: Glossopharyngeal nerve [IX]

Definition

Muhammad A. Javaid

Number: IX

Name: Glossopharyngeal

Sensory, motor, or both: Both sensory and motor

Origin/Target: Medulla

Nuclei: Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus

Function: Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils.

Description:

The glossopharyngeal nerve (CN IX) is the ninth cranial nerve and is classified as a mixed nerve, meaning it has both sensory and motor components as well as parasympathetic fibers. It is a versatile cranial nerve, participating in a variety of functions such as taste, salivation, swallowing, and helping regulate blood pressure.

Nuclei of the Glossopharyngeal Nerve:

The glossopharyngeal nerve arises from four key nuclei located in the medulla oblongata:

Nuclei

Description

Nucleus Ambiguus (Motor Nucleus)

Special visceral efferent motor fibers of the glossopharyngeal nerve arise from the nucleus ambiguus and innervate the stylopharyngeus muscle. The nucleus ambiguus receives bilateral cortical input (afferents) through corticonuclear fibers.

Inferior Salivatory Nucleus (Parasympathetic Nucleus)

The preganglionic parasympathetic fibers that arise from the inferior salivatory nucleus, run through the glossopharyngeal nerve and its branches to ultimately innervate the parotid gland via the otic ganglion.

Nucleus of the Solitary Tract (Sensory Nucleus)

The special visceral afferent neurons of the glossopharyngeal nerve transmit taste sensations from the posterior third of the tongue to the upper part of the nucleus of tractus solitarius, while the general visceral afferent neurons of the glossopharyngeal nerve from the carotid sinus and carotid body transmit information to the lower part of the nucleus of tractus solitarius. The latter plays an important role in reflexes such as the baroreceptor reflex for blood pressure regulation and chemoreception for blood gas levels.

Spinal Trigeminal Nucleus (Somatosensory Nucleus)

Processes general sensory input such as pain, temperature, and touch from the posterior one-third of the tongue, tonsils, pharynx, and middle ear.

Emergence and Course:

The glossopharyngeal nerve emerges as a series of rootlets from the anterolateral aspect of the upper medulla oblongata, in the groove between the olive and the inferior cerebellar peduncle. It proceeds laterally, exiting the skull via the jugular foramen, where it is accompanied by the vagus (CN X) and spinal accessory (CN XI) nerves.

Within the jugular foramen, it has two sensory ganglia: 1. Superior Ganglion: Primarily general somatic afferents, while 2. Inferior Ganglion: Contains visceral and taste afferents.

The nerve then descends through the neck, traveling between the internal carotid artery and internal jugular vein. It reaches the posterior surface of the stylopharyngeus muscle, which it innervates, before continuing towards the pharynx and tongue.

Branches of the Glossopharyngeal Nerve:

The nerve gives rise to several important branches along its course:

Branches

Description

Tympanic Nerve (Jacobson’s Nerve)

Carries parasympathetic fibers to the otic ganglion via the lesser petrosal nerve. Postganglionic fibers supply the parotid gland.

Stylopharyngeal Branch

Provides motor innervation to the stylopharyngeus muscle, which helps elevate the pharynx and larynx during swallowing and speech.

Carotid Sinus Nerve (Hering’s Nerve)

Innervates the carotid sinus (baroreceptors) and carotid body (chemoreceptors), playing a vital role in regulating blood pressure and gas composition.

Pharyngeal Branches

Contribute to the pharyngeal plexus (alongside vagus and sympathetic nerves), providing sensory input to the oropharynx and motor coordination for pharyngeal muscles.

Tonsillar Branches

Supply sensory fibers to the mucosa of the palatine tonsils.

Lingual Branches

Provide sensory and taste innervation to the posterior third of the tongue, including the vallate papillae.

Functions of the Glossopharyngeal Nerve:

The glossopharyngeal nerve participates in several key sensory, motor, and parasympathetic functions:

Type of function

Description

Motor Function

The CN-IX innervates the stylopharyngeus muscle, which elevates the pharynx and larynx during speaking and swallowing. - Example: During swallowing, this nerve helps coordinate muscle movements required to pass food from the mouth into the esophagus.

Parasympathetic Function

Provides secretomotor innervation to the parotid salivary gland through the otic ganglion. This ensures adequate saliva production, important for digestion and maintaining oral health.

Sensory Function

a)-Taste sensation: Conveys special sensory fibers for taste from the posterior third of the tongue.

b)-Visceral sensation: Detects changes in blood pressure (baroreceptors) and oxygen/carbon dioxide levels (chemoreceptors) from the carotid sinus and carotid body.

c)-General sensation: Supplies sensory fibers to the pharynx, posterior tongue, middle ear, and palatine tonsils.

Clinical Correlation; Injury to the Glossopharyngeal Nerve:

Dysfunction of the glossopharyngeal nerve can arise from trauma, tumors, vascular lesions, or surgical complications (e.g., after carotid endarterectomy). Common clinical presentations include:

  • Glossopharyngeal Neuralgia: Characterized by intense episodes of stabbing pain in the throat, tonsil area, or ear, often triggered by talking, swallowing, or coughing.

  • Impaired Taste and Sensation: Loss of taste on the posterior third of the tongue and reduced sensation in the oropharynx.

  • Swallowing Difficulties (Dysphagia): Weakness of the stylopharyngeus may impair swallowing, particularly the ability to elevate the pharynx and larynx.

  • Loss of Gag Reflex: The gag reflex involves both the glossopharyngeal nerve (sensory limb) and the vagus nerve (motor limb). Damage to CN IX can abolish this reflex.

  • Autonomic Dysfunction: Loss of baroreceptor input can affect blood pressure regulation, potentially causing symptoms of hemodynamic instability.

References

  • Snell, R.S. (2010). ‘Chapter 11: The cranial nerve nuclei and their central connections and distribution’, in Clinical Neuroanatomy. (7th ed.) Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, pp. 350-352.

  • Thomas K, Minutello K, Das JM. Neuroanatomy, Cranial Nerve 9 (Glossopharyngeal) [Updated 2022 Nov 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/sites/books/NBK539877/

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