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.