From the anterior portion of the
medulla oblongata, the glossopharyngeal nerve passes laterally across or below the
flocculus, and leaves the skull through the central part of the
jugular foramen. From the superior and inferior ganglia in jugular foramen, it has its own sheath of
dura mater. The inferior ganglion on the inferior surface of petrous part of temporal is related with a triangular depression into which the aqueduct of cochlea opens. On the inferior side, the glossopharyngeal nerve is lateral and anterior to the
vagus nerve and
accessory nerve. In its passage through the foramen (with X and XI), the glossopharyngeal nerve passes between the
internal jugular vein and
internal carotid artery. It descends in front of the latter vessel and beneath the
styloid process and the muscles connected with it, to the posterior lower border of the
stylopharyngeus muscle. It then curves forward, forming an arch on the side of the neck and lying upon the
stylopharyngeus and
middle pharyngeal constrictor muscle. From there, it passes under cover of the
hyoglossus muscle and is finally distributed to the
palatine tonsil, the
mucous membrane of the
fauces and base of the
tongue, and the serous glands of the
mouth.
Branches •
tympanic nerve •
stylopharyngeal nerve •
tonsillar nerve •
carotid sinus nerve • Branches to the
posterior third of tongue •
lingual branches • A communicating branch to the
vagus nerve Note: The glossopharyngeal nerve contributes in the formation of the
pharyngeal plexus along with the vagus nerve. The glossopharyngeal nerve has five distinct general functions: • Branchial motor (
special visceral efferent)supplies the
stylopharyngeus muscle. • Visceral motor (
general visceral efferent)provides
parasympathetic innervation of the
parotid gland via the otic ganglion • Visceral sensory (
general visceral afferent)carries visceral sensory information from the
carotid sinus and
carotid body. • General sensory (
general somatic afferent)provides general sensory information from inner surface of the
tympanic membrane, upper
pharynx (GVA), and the posterior one-third of the
tongue. • Visceral afferent (
special visceral afferent)provides
taste sensation from the posterior one-third of the
tongue, including
circumvallate papillae. The glossopharyngeal nerve as noted above is a mixed nerve consisting of both sensory and motor nerve fibers. The sensory fibers' origin include the pharynx, middle ear, posterior one-third of the tongue (including taste buds); and the carotid body and sinus. These fibers terminate at the
medulla oblongata. The motor fibers' origin is the medulla oblongata, and they terminate at the parotid salivary gland, the glands of the posterior tongue, and the
stylopharyngeus muscle (which dilates the pharynx during swallowing).
Overview of branchial motor component The
branchial motor component of CN IX provides voluntary control of the stylopharyngeus muscle, which elevates the pharynx during swallowing and speech.
Origin and central course The branchial motor component originates from the
nucleus ambiguus in the reticular formation of the rostral
medulla. Fibers leaving the nucleus ambiguus travel anteriorly and laterally to exit the medulla, along with the other components of CN IX, between the olive and the
inferior cerebellar peduncle.
Intracranial course Upon emerging from the lateral aspect of the medulla the branchial motor component joins the other components of CN IX to exit the skull via the jugular foramen. The glossopharyngeal fibers travel just anterior to the cranial nerves X and XI, which also exit the skull via the
jugular foramen.
Extra-cranial course and final innervation Upon exiting the skull the branchial motor fibers descend deep to the
temporal styloid process and wrap around the posterior border of the
stylopharyngeus muscle before innervating it.
Voluntary control of the stylopharyngeus muscle Signals for the voluntary movement of
stylopharyngeus muscle originate in the pre-motor and motor cortex (in association with other cortical areas) and pass via the
corticobulbar tract in the genu of the internal capsule to synapse bilaterally on the ambiguus nuclei in the medulla.
Overview of visceral motor component Parasympathetic component of the glossopharyngeal nerve that innervates the ipsilateral parotid gland.
Origin and central course The
preganglionic nerve fibers originate in the
inferior salivatory nucleus of the rostral medulla and travel anteriorly and laterally to exit the brainstem between the
medullary olive and the
inferior cerebellar peduncle with the other components of CN IX. Note: These neurons do not form a distinct nucleus visible on cross-section of the brainstem. The position indicated on the diagram is representative of the location of the cell bodies of these fibers.
Intracranial course Upon emerging from the lateral aspect of the medulla, the
visceral motor fibers join the other components of CN IX to enter the
jugular foramen. Within the jugular foramen, there are two glossopharyngeal ganglia that contain nerve cell bodies that mediate general, visceral, and special sensation. The visceral motor fibers pass through both ganglia without synapsing and exit the inferior ganglion with CN IX general sensory fibers as the
tympanic nerve. Before exiting the jugular foramen, the tympanic nerve enters the
petrous portion of the temporal bone and ascends via the
inferior tympanic canaliculus to the
tympanic cavity. Within the tympanic cavity the tympanic nerve forms a
plexus on the surface of the
promontory of the middle ear to provide general sensation. The visceral motor fibers pass through this plexus and merge to become the
lesser petrosal nerve. The lesser petrosal nerve re-enters and travels through the temporal bone to emerge in the
middle cranial fossa just lateral to the
greater petrosal nerve. It then proceeds anteriorly to exit the skull via the
foramen ovale along with the
mandibular nerve component of CN V (V3).
Extra-cranial course and final innervations Upon exiting the skull, the lesser petrosal nerve synapses in the
otic ganglion, which is suspended from the
mandibular nerve immediately below the
foramen ovale. Postganglionic fibers from the otic ganglion travel with the
auriculotemporal branch of CN V3 to enter the substance of the
parotid gland.
Hypothalamic Influence Fibers from the
hypothalamus and
olfactory system project via the
dorsal longitudinal fasciculus to influence the output of the
inferior salivatory nucleus. Examples include: 1) dry mouth in response to fear (mediated by the hypothalamus); 2) salivation in response to smelling food (mediated by the olfactory system)
Overview of visceral sensory component This component of CN IX innervates the baroreceptors of the
carotid sinus and chemoreceptors of the
carotid body. ;Peripheral and intracranial course. :Sensory fibers arise from the
carotid sinus and
carotid body at the common carotid artery bifurcation, ascend in the
carotid sinus nerve, and join the other components of
CN IX at the inferior glossopharyngeal ganglion. The cell bodies of these neurons reside in the
inferior glossopharyngeal ganglion. The central processes of these neurons enter the skull via the
jugular foramen. ;Central course – visceral sensory component :Once inside the skull, the visceral sensory fibers enter the lateral medulla between the olive and the
inferior cerebellar peduncle and descend in the
solitary tract to synapse in the caudal
solitary nucleus. From the solitary nucleus, connections are made with several areas in the reticular formation and
hypothalamus to mediate cardiovascular and respiratory reflex responses to changes in blood pressure, and serum concentrations of CO2 and O2.
Clinical correlation The visceral sensory fibers of CN IX mediate the afferent limb of the pharyngeal reflex in which touching the back of the pharynx stimulates the patient to gag (i.e., the gag reflex). The efferent signal to the musculature of the pharynx is carried by the branchial motor fibers of the vagus nerve.
Overview of somatic sensory component This component of CN IX carries general sensory information (pain, temperature, and touch) from the skin of the external ear, internal surface of the tympanic membrane, the walls of the upper pharynx, and the posterior one-third of the tongue, anterior surface of the epiglottis, vallecula. ;Peripheral course :Sensory fibers from the skin of the external ear initially travel with the auricular branch of CN X, while those from the middle ear travel in the tympanic nerve as discussed above (CN IX visceral motor section). General sensory information from the upper pharynx and posterior one-third of the tongue travel via the pharyngeal branches of CN IX. These peripheral processes have their cell body in either the superior or inferior glossopharyngeal ganglion. ;Central course :The central processes of the general sensory neurons exit the glossopharyngeal ganglia and pass through the jugular foramen to enter the brainstem at the level of the medulla. Upon entering the medulla these fibers descend in the spinal trigeminal tract and synapse in the caudal spinal nucleus of the trigeminal.
Overview of special sensory component The special sensory component of CN IX provides taste sensation from the posterior one-third of the tongue. ;Peripheral course :Special sensory fibers from the posterior one-third of the tongue travel via the pharyngeal branches of CN IX to the inferior glossopharyngeal ganglion where their cell bodies reside. ;Central course – special sensory component :The central processes of these neurons exit the inferior ganglion and pass through the jugular foramen to enter the brainstem at the level of the rostral medulla between the olive and inferior cerebellar peduncle. Upon entering the medulla, these fibers ascend in the tractus solitarius and synapse in the gustatory part of nucleus solitarius. Taste fibers from CN VII and X also ascend and synapse here. Ascending secondary neurons originating in nucleus solitarius project bilaterally to the ventral posteromedial (VPM) nuclei of the thalamus via the central tegmental tract. Tertiary neurons from the thalamus project via the posterior limb of the internal capsule to the inferior one-third of the primary sensory cortex (the gustatory cortex of the parietal lobe).
Associated brainstem nuclei •
Solitary nucleus: 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: 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:
lower motor neurons for the
stylopharyngeus muscle •
Inferior salivatory nucleus: preganglionic
parasympathetic neurons to the otic ganglion and then to the parotid gland ==Functions==