Origin and skull exit
At the brainstem level, the glossopharyngeal nerve emerges from the medulla oblongata. It exits via 4–6 rootlets posterior to the olive, located just inferior to the vestibulocochlear nerve (VIII pair).
The nerve leaves the cranial cavity through the anterior part of the jugular foramen. It is right here, in the region of the foramen, that two clusters of sensory neuron cell bodies are formed:
- Superior ganglion (ganglion superius) — located directly within the foramen itself.
- Inferior ganglion (ganglion inferius) — located slightly lower, on the surface of the petrous part of the temporal bone.
Further down at the base of the skull, the nerve descends, passing between the internal carotid artery and the internal jugular vein. It then forms an arch, directed anteriorly and slightly superiorly, penetrating into the substance of the root of the tongue.
Nuclei and functional composition
Being a mixed nerve, the glossopharyngeal nerve contains three types of fibers associated with different brainstem nuclei:
- Motor fibers. These are axons of cells of the somatic nucleus ambiguus. They are responsible for the innervation of just a single muscle — the stylopharyngeus (m. stylopharyngeus).
- Sensory fibers. These are processes of cells of the superior and inferior ganglia. Their peripheral processes gather information from organs, while the central processes penetrate the medulla oblongata, where they terminate on cells of the nucleus of the solitary tract (tractus solitarius). Some of them also reach the upper part of the dorsal nucleus of the vagus nerve.
- Parasympathetic (secretory) fibers. Originate from the autonomic inferior salivatory nucleus. Leaving the brain, they join the composition of the tympanic nerve.
Main branches of the glossopharyngeal nerve
Along its pathway, the nerve gives off a number of important branches that ensure the function of the pharynx, tongue, and vascular reflexogenic zones:
- Lingual branches (rr. linguales) — terminal branches of the nerve. They ramify in the mucous membrane of the posterior third of the tongue (from the epiglottis to the vallate papillae). They carry taste impulses and general sensation fibers. They communicate with the lingual nerve (from the V pair) and branches of the opposite side.
- Pharyngeal branches (rr. pharyngei) — 3–4 trunks originating in the interval between the external and internal carotid arteries. They run to the lateral wall of the pharynx, where they participate in the formation of the pharyngeal plexus.
- Tonsillar branches (rr. tonsillares) — short branches (3–5 in number) ascending to the mucous membrane of the palatine arches and tonsils.
- Carotid sinus branch (r. sinus carotici) — a crucial nerve for blood pressure regulation. It intertwines into the wall of the carotid sinus and the substance of the carotid body.
- Branch to the stylopharyngeus muscle (r. musculi stylopharyngei) — a motor branch entering the muscle via several trunks.
- Communicating branch — connects the superior ganglion of the IX pair with the auricular branch of the vagus nerve, passing within the substance of the temporal bone.
Tympanic nerve and its pathway
Special attention is deserved by the tympanic nerve (n. tympanicus). It arises from the inferior ganglion and contains sensory and parasympathetic fibers.
Having entered the tympanic cavity of the middle ear, it runs along its medial wall, forming the tympanic plexus (tympanic ganglion). Together with the sympathetic fibers of the caroticotympanic nerves, it forms the tympanic plexus (plexus tympanicus). This plexus innervates the mucous membrane of the tympanic cavity, the tympanic membrane, the mastoid air cells, and gives off the tubal branch to the auditory tube.
The continuation of the parasympathetic fibers of the tympanic plexus is the lesser petrosal nerve (n. petrosus minor). It leaves the tympanic cavity, exits the skull through the sphenopetrosal fissure, and heads toward the otic ganglion, where it forms its parasympathetic root.
Briefly: answers to topical questions
Where are the nuclei of the glossopharyngeal nerve projected in the rhomboid fossa?
The nuclei of the glossopharyngeal nerve are projected onto the superior triangle of the rhomboid fossa, which is located in the region of the pons.
In the topography of the gray matter of the rhomboid fossa, the nuclei are distributed in functional columns:
- Autonomic nuclei — occupy the middle column, lying between the somatic sensory and motor nuclei.
Which salivary gland is innervated by the parasympathetic fibers of the glossopharyngeal nerve?
The parasympathetic fibers of the glossopharyngeal nerve innervate the parotid salivary gland.
These efferent fibers form the following pathway:
- Inferior salivatory nucleus (nucleus salivatorius inferior) — serves as the source of preganglionic fibers.
- Lesser petrosal nerve (n. petrosus minor) — carries parasympathetic fibers to the site of synapse.
- Otic ganglion (ganglion oticum) — a parasympathetic ganglion where impulse transmission occurs, after which the fibers proceed to the target organ.
Which nerves participate in the formation of the pharyngeal plexus?
Branches of cranial nerves and the autonomic nervous system participate in the formation of the pharyngeal plexus (plexus nervosus pharyngis).
Its formation involves:
- Glossopharyngeal nerve (n. glossopharyngeus) — gives off 3–4 pharyngeal branches (rr. pharyngei) that run toward the lateral wall of the pharynx.
- Vagus nerve (n. vagus) — gives off pharyngeal branches accompanying the fibers of the IX pair.
- Sympathetic trunk (truncus sympathicus) — its fibers join the branches of the cranial nerves.
For memorizing the nuclei of the IX pair: motor — ambiguus (shared with the vagus nerve), parasympathetic — inferior salivatory, sensory — solitary tract.
Class and exam questions
Where are the cell bodies of sensory neurons of the glossopharyngeal nerve located?
In the superior and inferior ganglia (ganglion superius et inferius), which are located in the region of the jugular foramen of the skull.
Which part of the tongue is innervated by the IX pair?
The posterior third of the tongue. The nerve transmits both general and taste sensation from the root of the tongue all the way to the vallate papillae.
What is the carotid sinus branch and what is its function?
This is a branch running to the carotid sinus and body. It gathers information from baroreceptors and chemoreceptors, participating in the reflex regulation of blood pressure.
Where does the lesser petrosal nerve go?
The lesser petrosal nerve, containing parasympathetic fibers from the tympanic plexus, heads toward the otic ganglion.
What else to study on this topic
- Topography of the glossopharyngeal nerve in the pharyngeal wall
- Formation and composition of the pharyngeal plexus
- Connection of taste fibers of the IX pair with the thalamus and cerebral cortex
- Tympanic plexus: interaction with the greater petrosal nerve
- Autonomic innervation of salivary glands via the otic ganglion
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