The glossopharyngeal nerve, known as the ninth cranial nerve, is a mixed nerve
that carries afferent sensory and efferent motor information. It exits the
brainstem out from the sides of the upper medulla, just rostral to the vagus
nerve. The motor division of the glossopharyngeal nerve is derived from
the basal plate of the embryonic medulla oblongata, while the sensory division
originates from the cranial neural crest.
Structure 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, 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 lower border of the stylopharyngeus. 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 Stylopharyngeal
Tonsillar Nerve to carotid sinus
Branches to the posterior third of tongue
Lingual branches A communicating branch to the Vagus
nerve Note: The glossopharyneal nerve
contributes in the formation of the pharyngeal plexus along with the vagus
nerve. The glossopharyngeal nerve has five
distinct general functions: Branchial motor – supplies the
stylopharyngeus muscle. Visceral motor – provides
parasympathetic innervation of the parotid gland via the otic ganglion]
Visceral sensory – carries visceral sensory information from the carotid
sinus and carotid body. General sensory – provides general
sensory information from inner surface of the tympanic membrane, upper pharynx,
and the posterior one-third of the tongue.
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; 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.
= 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 medulla
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 and pass via
the corticobulbar tract in the posterior limb 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. 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; 2) salivation in response to smelling food
= 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 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 tractus solitarius to synapse in the
caudal nucleus solitarius. From the nucleus solitarius, 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. = Overview of general sensory component
This component of CN IX carries general sensory information 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.
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.
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 cell their cell body in either the superior or inferior
glossopharyngeal ganglion. Central course - general sensory
component. 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. Central course - general sensory
component Ascending secondary neurons originating
from the spinal nucleus of CN V project to the contralateral ventral
posteromedial nucleus of the thalamus via the anterolateral system. Tertiary
neurons from the thalamus project via the posterior limb of the internal
capsule to the sensory cortex of the post-central gyrus.
Clinical correlation. The general 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. The efferent signal to the musculature
of the pharynx is carried by the branchial motor fibers of the vagus
nerve. = 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 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.
= Brainstem connections = The glossopharyngeal nerve is mostly
sensory. The glossopharyngeal nerve also aids in tasting, swallowing and salivary
secretions. Its superior and inferior ganglia contain the cell bodies of pain
fibers. It also projects into many different structures in the brainstem:
Solitary nucleus: Taste from the posterior one-third of the tongue and
information from carotid baroreceptors and carotid body chemoreceptors
Spinal nucleus of the trigeminal nerve: Somatic sensory fibers from the middle
ear Lateral Nucleus of Ala Cinerea: Visceral
pain Nucleus ambiguus: The lower motor
neurons for the stylopharyngeus muscle Inferior salivatory nucleus:
Parasympathetic input to the parotid and mucous glands.
Functions There are a number of functions of the
glossopharyngeal nerve: It receives general sensory fibers from
the tonsils, the pharynx, the middle ear and the posterior 1/3 of the tongue.
It receives special sensory fibers from the posterior one-third of the tongue.
It receives visceral sensory fibers from the carotid bodies, carotid sinus.
It supplies parasympathetic fibers to the parotid gland via the otic ganglion.
It supplies motor fibers to stylopharyngeus muscle, the only motor
component of this cranial nerve. It contributes to the pharyngeal plexus.
Clinical significance = Damage =
The glossopharyngeal nerve if damaged can have several effects on the human
body. These effects include loss of bitter and sour taste, and impaired
swallowing. = Examination =
The clinical tests used to determine if the glossopharyngeal nerve has been
damaged include testing the gag reflex of the mouth, asking the patient to
swallow or cough, and evaluating for speech impediments. The clinician may
also test the posterior one-third of the tongue with bitter and sour substances
to evaluate for impairment of taste. The integrity of the glossopharyngeal
nerve may be evaluated by testing the patient's general sensation and that of
taste on the posterior third of the tongue. The gag reflex can also be used
to evaluate the glossphyaryngeal nerve, but also tests the vagus nerve, as only
the afferent fibres involved in the reflex are carried by the
glossopharyngeal nerve. Additional images
References Saladin, Anatomy and Physiology: The
Unity of Form and Function, 6th edition External links
hier-698 at NeuroNames MedEd at Loyola GrossAnatomycncn9.htm
MedlinePlus Image 9350 cranialnerves at The Anatomy Lesson by
Wesley Norman Notes on Glossopharyngeal Nerve