| Glossopharyngeal nerve | |
|---|---|
 Plan of the upper portions of the glossopharyngeal,vagus, andaccessory nerves. | |
 Course and distribution of the glossopharyngeal,vagus, andaccessory nerves. (Label for glossopharyngeal is at upper left.) | |
| Details | |
| To | Tympanic nerve |
| Innervates | Motor:stylopharyngeus Sensory:Oropharynx,Eustachian tube,middle ear, posterior third oftongue,carotid sinus,carotid body Special sensory:Taste to posterior third of tongue |
| Identifiers | |
| Latin | nervus glossopharyngeus |
| MeSH | D005930 |
| NeuroNames | 701,793 |
| NeuroLex ID | birnlex_1274 |
| TA98 | A14.2.01.135 |
| TA2 | 6320 |
| FMA | 50870 |
| Anatomical terms of neuroanatomy | |
| Cranial nerves |
|---|
|
Theglossopharyngeal nerve (/ˌɡlɒsoʊfəˈrɪn(d)ʒiəl,-ˌfærənˈdʒiːəl/[1]), also known as theninth cranial nerve,cranial nerve IX, or simplyCN IX,[2] is acranial nerve that exits thebrainstem from the sides of the uppermedulla, just anterior (closer to thenose) to thevagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from thebasal plate of theembryonicmedulla oblongata, whereas the sensory division originates from thecranial neural crest.
From the anterior portion of themedulla oblongata, the glossopharyngeal nerve passes laterally across or below theflocculus, and leaves the skull through the central part of thejugular foramen. From the superior and inferior ganglia in jugular foramen, it has its own sheath ofdura 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 thevagus nerve andaccessory nerve.
In its passage through the foramen (with X and XI), the glossopharyngeal nerve passes between theinternal jugular vein andinternal carotid artery.[3] It descends in front of the latter vessel and beneath thestyloid process and the muscles connected with it, to the posterior lower border of thestylopharyngeus muscle.[4] It then curves forward, forming an arch on the side of the neck and lying upon thestylopharyngeus andmiddle pharyngeal constrictor muscle. From there, it passes under cover of thehyoglossus muscle and is finally distributed to thepalatine tonsil, themucous membrane of thefauces and base of thetongue, and the serous glands of themouth.
Note: The glossopharyngeal nerve contributes in the formation of thepharyngeal plexus along with the vagus nerve.
The glossopharyngeal nerve has five distinct general functions:
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 themedulla oblongata. The motor fibers' origin is the medulla oblongata, and they terminate at the parotid salivary gland, the glands of the posterior tongue, and thestylopharyngeus muscle (which dilates the pharynx during swallowing).
Thebranchial 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 thenucleus ambiguus in the reticular formation of the rostralmedulla. 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 theinferior 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 thejugular foramen.
Extra-cranial course and final innervation
Upon exiting the skull the branchial motor fibers descend deep to thetemporal styloid process and wrap around the posterior border of thestylopharyngeus muscle before innervating it.
Voluntary control of the stylopharyngeus muscle
Signals for the voluntary movement ofstylopharyngeus muscle originate in the pre-motor and motor cortex (in association with other cortical areas) and pass via thecorticobulbar tract in the genu of the internal capsule to synapse bilaterally on the ambiguus nuclei in the medulla.
Parasympathetic component of the glossopharyngeal nerve that innervates the ipsilateral parotid gland.
Origin and central course
Thepreganglionic nerve fibers originate in theinferior salivatory nucleus of the rostral medulla and travel anteriorly and laterally to exit the brainstem between themedullary olive and theinferior 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, thevisceral motor fibers join the other components of CN IX to enter thejugular 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 thetympanic nerve. Before exiting the jugular foramen, the tympanic nerve enters thepetrous portion of the temporal bone and ascends via theinferior tympanic canaliculus to thetympanic cavity. Within the tympanic cavity the tympanic nerve forms aplexus on the surface of thepromontory of the middle ear to provide general sensation. The visceral motor fibers pass through this plexus and merge to become thelesser petrosal nerve. The lesser petrosal nerve re-enters and travels through the temporal bone to emerge in themiddle cranial fossa just lateral to thegreater petrosal nerve. It then proceeds anteriorly to exit the skull via theforamen ovale along with themandibular nerve component of CN V (V3).
Extra-cranial course and final innervations
Upon exiting the skull, the lesser petrosal nerve synapses in theotic ganglion, which is suspended from themandibular nerve immediately below theforamen ovale. Postganglionic fibers from the otic ganglion travel with theauriculotemporal branch of CN V3 to enter the substance of theparotid gland.
Hypothalamic Influence
Fibers from thehypothalamus andolfactory system project via thedorsal longitudinal fasciculus to influence the output of theinferior 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)
This component of CN IX innervates the baroreceptors of thecarotid sinus and chemoreceptors of thecarotid body.
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.[5]
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.
The special sensory component of CN IX provides taste sensation from the posterior one-third of the tongue.
Damage to the glossopharyngeal nerve can result in loss of taste sensation to the posterior one third of the tongue, and impairedswallowing.
The clinical tests used to determine if the glossopharyngeal nerve has been damaged include testing thegag reflex of the mouth, asking the patient toswallow orcough, 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 glossopharyngeal nerve.
{{cite book}}: CS1 maint: location missing publisher (link)Saladin, Anatomy and Physiology: The Unity of Form and Function, 6th edition
