Glossopharyngeal Nerve Overview

Glossopharyngeal Nerve Overview

• Originates from the anterior jugular foramen, lateral to the inferior petrosal sinus.
• Forms a notch in the inferior petrous bone, where its inferior ganglion widens the nerve.
• The superior ganglion is part of the inferior ganglion.
• Passes down next to the internal carotid artery and curves around stylopharyngeus muscle.
• Descends behind the hyoglossus muscle to reach the tongue.
• Contains six branches: tympanic (Jacobson's), motor to stylopharyngeus, carotid sinus, pharyngeal, tonsillar, and lingual.

Tympanic Branch

• Leaves the inferior ganglion.
• Passes through the tympanic canaliculus.
• Supplies middle ear, mastoid air cells, and the bony part of the auditory tube with sensory fibers.
• Contains parasympathetic fibers from the inferior salivary nucleus.
• Enters the tympanic plexus on the promontory.
• Joins the lesser petrosal nerve to relay at the otic ganglion for parotid gland secretomotor supply.

Motor Branch to Stylopharyngeus

• Supplies stylopharyngeus muscle.
• Motor axons originate from the nucleus ambiguus.

Carotid Sinus Nerve

• Primary supply of the carotid sinus and carotid body (baroreceptors & chemoreceptors).
• Critical for connections with vasomotor and autonomic centers in the brainstem's reticular formation via the nucleus of the tractus solitarius.

Pharyngeal Branches

• Joins the pharyngeal plexus on the middle constrictor muscle.
• Supplies oropharyngeal mucosa with common sensation, taste, and parasympathetic fibers (relayed in small ganglia in the pharynx) to its mucous and serous glands.

Tonsillar Branch

• Supplies the palatine tonsil's mucosa.
• Interconnects with the lesser palatine nerves.

Lingual Branch

• Supplies posterior one-third of the tongue with sensory fibers (common sensation and taste).
• Provides secretomotor fibers to posterior tongue glands (relayed in lingual ganglia within the mucosa).

Glossopharyngeal Nerve Nuclei

• Composed of two motor and two sensory nuclei.
• Motor :
  • Branchial (nucleus ambiguus) for stylopharyngeus.
  • Visceral (inferior salivary nucleus) for otic ganglion and parotid secretion.
• Sensory :
  • Visceral (nucleus of tractus solitarius) for taste (posterior tongue), carotid body + sinus (blood pressure/chemoreceptors).
  • Somatic (trigeminal nerve) for general sensation (tongue, palate, pharynx, tonsil).

Glossopharyngeal Nerve Traversing the Skull

• Emerges from the medulla oblongata between the inferior cerebellar peduncle and the olive.
• Travels laterally behind the jugular tubercle, entering the anterior compartment of the jugular foramen.
• Lies lateral to the inferior petrosal sinus.
• Passes through arachnoid and dura mater, creating an elongated inferior ganglion with sensory neuron cell bodies.
• Enters the middle ear via the tympanic canaliculus.

Lesser Petrosal Nerve

• A branch of the glossopharyngeal nerve
• Carries preganglionic parasympathetic fibers from the inferior salivary nucleus to the otic ganglion for parotid gland secretomotor supply
• Emerges through the foramen ovale to reach the otic ganglion.

Nerve Supply to Other Structures

• Middle Ear Mucosa: Tympanic plexus (formed by the Tympanic branch of the glossopharyngeal nerve).
• Pharyngeal Muscles: Mostly supplied by the pharyngeal plexus (vagus and glossopharyngeal nerves). Stylopharyngeus, however, is the only muscle supplied directly by the glossopharyngeal nerve.
• Oropharynx Mucosa: Mostly glossopharyngeal nerve. Exceptions include: cricopharyngeus (potentially recurrent laryngeal or external laryngeal), nasopharynx (maxillary nerve via pterygopalatine ganglion).
• Vallate Papillae: Supplied by the glossopharyngeal nerve, including common sensibility and taste fibers.

Glossopharyngeal Lesions

• Rare, often occur with other cranial nerve damage, e.g. in posterior fossa tumors.
• Functional testing primarily involves checking taste sensation on the posterior tongue (as stylopharyngeus has no independently testable function).

Glossopharyngeal, Vagus, and Accessory Nerves

• Arise from the medulla oblongata as rootlets, between the inferior cerebellar peduncle and olive.
• Pass laterally across the occipital bone (glossopharyngeal first, then vagus, then accessory).
• Pass through the jugular foramen together.
• Distinctive relationships within the jugular foramen (glossopharyngeal and accessory more lateral relative to the vagus).

Internal Carotid Artery

• Arises from the common carotid artery.
• Begins at a slight bulge called the carotid sinus, rich with baroreceptors supplied by the glossopharyngeal nerve.
• The carotid body, positioned behind the bifurcation, is a chemoreceptor containing glomus cells innervated by the glossopharyngeal.
• The internal carotid artery sits medial to the external carotid artery and curves posteriorly towards the base of the skull.
• Is embedded in the carotid sheath, behind which lies the sympathetic trunk and pharyngeal veins.

Second Pharyngeal Pouch Development

• Contributing to the tympanic cavity development
• The glossopharyngeal nerve's tympanic branch and tonsillar crypts are associated with the second pouch's derivatives.

Otic Ganglion

• A small relay station for parasympathetic secretomotor fibers to the parotid gland via the lesser petrosal nerve.
• Located near the foramen ovale, between the tensor palati and the mandibular nerve.

Explore the glossopharyngeal nerve, its origin, branches, and functions. This quiz provides insight into the anatomy, including the tympanic branch and its role in sensory and motor supply. Test your knowledge on the intricacies of this important cranial nerve.