Structure and Branches of the Glossopharyngeal Nerve
- Glossopharyngeal nerve passes laterally across or below the flocculus
- Leaves the skull through the central part of the jugular foramen
- Has its own sheath of dura mater from the superior and inferior ganglia in jugular foramen
- Inferior ganglion is related to a triangular depression into which the aqueduct of cochlea opens
- Glossopharyngeal nerve is lateral and anterior to the vagus nerve and accessory nerve
- Branches include the tympanic nerve, stylopharyngeal nerve, tonsillar nerve, carotid sinus nerve, branches to the posterior third of the tongue, lingual branches, a communicating branch to the vagus nerve, and contribution to the pharyngeal plexus with the vagus nerve

Overview of Motor Components of the Glossopharyngeal Nerve
- Branchial motor component controls the stylopharyngeus muscle
- Originates from the nucleus ambiguus in the rostral medulla
- Fibers exit the medulla between the olive and the inferior cerebellar peduncle
- Joins other components of CN IX to exit the skull via the jugular foramen
- Innervates the stylopharyngeus muscle to elevate the pharynx during swallowing and speech
- Visceral motor component innervates the ipsilateral parotid gland
- Preganglionic fibers originate in the inferior salivatory nucleus of the rostral medulla
- Fibers exit the brainstem between the medullary olive and the inferior cerebellar peduncle
- Pass through glossopharyngeal ganglia without synapsing
- Lesser petrosal nerve carries the fibers to the otic ganglion and parotid gland

Overview of Sensory Components of the Glossopharyngeal Nerve
- Visceral sensory component innervates the baroreceptors of the carotid sinus and chemoreceptors of the carotid body
- Sensory fibers arise from the carotid sinus and carotid body at the common carotid artery bifurcation
- Join other components of CN IX at the inferior glossopharyngeal ganglion
- Central processes of these neurons enter the skull via the jugular foramen
- Mediates cardiovascular and respiratory reflex responses to changes in blood pressure, CO2, and O2 levels
- Somatic sensory component carries general sensory information from the skin of the external ear, internal surface of the tympanic membrane, walls of the upper pharynx, and posterior one-third of the tongue, anterior surface of the epiglottis, vallecula
- Special sensory component provides taste sensation from the posterior one-third of the tongue

Associated Brainstem Nuclei of the Glossopharyngeal Nerve
- Solitary nucleus: receives taste from the posterior 1/3 of the tongue and information from carotid sinus baroreceptors and carotid body chemoreceptors
- Spinal nucleus of the trigeminal nerve: receives somatic sensory fibers from the internal surface of the tympanic membrane, middle ear, upper part of the pharynx, soft palate, and posterior 1/3 of the tongue
- Nucleus ambiguus: contains lower motor neurons for the stylopharyngeus muscle
- Inferior salivatory nucleus: contains preganglionic parasympathetic neurons to the otic ganglion and then to the parotid gland

Functions and Clinical Significance of the Glossopharyngeal Nerve
- Receives general somatic sensory fibers from the tonsils, pharynx, middle ear, and posterior 1/3 of the tongue
- Receives special visceral sensory fibers (taste) from the posterior 1/3 of the tongue
- Receives visceral sensory fibers from the carotid bodies and carotid sinus
- Supplies parasympathetic fibers to the parotid gland via the otic ganglion
- Supplies motor fibers to the stylopharyngeus muscle and contributes to the pharyngeal plexus
- Damage to the glossopharyngeal nerve can result in loss of taste sensation to the posterior one-third of the tongue and impaired swallowing
- Clinical tests to determine damage include testing the gag reflex, swallowing or coughing, and evaluating speech impediments
- The integrity of the glossopharyngeal nerve may be evaluated by testing general sensation and taste on the posterior third of the tongue
- The gag reflex can also be used to evaluate the glossopharyngeal nerve.