The glossopharyngeal nerve is the ninth (IX) of twelve pairs of cranial nerves

Cranial nerves

Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...

 (24 nerves total). It exits the brainstem out from the sides of the upper medulla

Medulla oblongata

The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...

, just rostral (closer to the nose) to the vagus nerve

Vagus nerve

The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...

. The motor division of the glossopharyngeal nerve is derived from the basal plate

Basal plate (neural tube)

In the developing nervous system, the basal plate is the region of the neural tube ventral to the sulcus limitans. It extends from the rostral mesencephalon to the end of the spinal cord and contains primarily motor neurons, whereas neurons found in the alar plate are primarily associated with...

 of the embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

nic medulla oblongata

Medulla oblongata

The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...

, while the sensory division originates from the cranial neural crest

Cranial neural crest

The cranial neural crest is a form of neural crest.The cranial neural crest arises in the anterior and populates the face and the pharyngeal arches giving rise to bones, cartilage, nerves and connective tissue...

.

Functions

There are a number of functions of the glossopharyngeal nerve:

• It receives general sensory fibers (ventral trigeminothalamic tract
  Ventral trigeminothalamic tract
  The Anterior trigeminothalamic tract serves as pain, temperature, and crude touch pathway from the face, head and neck. It receives input from trigeminal nerve, facial nerve, glossopharyngeal nerve and vagus nerve...
  
  ) from the tonsils, the pharynx
  Pharynx
  The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
  
  , the middle ear
  Middle ear
  The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
  
   and the posterior 1/3 of the tongue.
• It receives special sensory fibers (taste
  Taste
  Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
  
  ) from the posterior one-third of the tongue
  Tongue
  The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
  
  .
• It receives visceral sensory fibers from the carotid bodies.
• It supplies parasympathetic fibers to the parotid gland
  Parotid gland
  The paired parotid glands are the largest of the salivary glands. They are each found wrapped around the mandibular ramus, and secrete saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches.-Location:The parotid glands...
  
   via the otic ganglion
  Otic ganglion
  The otic ganglion is a small, oval shaped, flattened parasympathetic ganglion of a reddish-gray color, located immediately below the foramen ovale in the infratemporal fossa. It gives innervation to the parotid gland for salivation....
  
  .
• It supplies motor fibers to stylopharyngeus muscle
  Stylopharyngeus muscle
  The stylopharyngeus is a muscle in the head that stretches between the styloid process and the pharynx.-Structure:The stylopharyngeus is a long, slender muscle, cylindrical above, flattened below...
  
  , the only motor component of this cranial nerve.
• It contributes to the pharyngeal plexus
  Pharyngeal plexus
  Pharyngeal plexus can refer to:* Pharyngeal plexus of vagus nerve* Pharyngeal plexus...
  
  .

Glossopharyngeal Overview

The glossopharyngeal nerve consists of five components with distinct functions: Branchial motor (special visceral efferent) - supplies the stylopharyngeus muscle. Visceral motor (general visceral efferent) provides parasympathetic innervation of the parotid gland. Visceral sensory (general visceral afferent) carries visceral sensory information from the carotid sinus and body. General sensory (general somatic afferent) provides general sensory information from the skin of the external ear, internal surface of the tympanic membrane, upper pharynx, and the posterior one-third of the tongue. Special sensory (special afferent) provides taste sensation from the posterior one-third of the tongue.

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 - Branchial Motor Component. 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 - Branchial Motor Component. 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 styloid process and wrap around the posterior border of the stylopharyngeus muscle before innervating it. Branchial motor component - 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 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 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 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 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 bifurcation of the common carotid artery, ascend in the sinus nerve, and join the other components of CN IX at the inferior hypoglossal ganglion. The cell bodies of these neurons reside in the inferior 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 (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.
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 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 (VPM) nucleus of the thalamus via the anterolateral system (ventral trigeminothalamic tract). 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 (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 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 caudal 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).

Brainstem connections

The glossopharyngeal nerve is mostly sensory. The glossopharyngeal nerve also aids in tasting, swallowing and salivary secretions. Its superior and inferior (petrous) ganglia contain the cell bodies of pain fibers. It also projects into many different structures in the brainstem:

• Solitary nucleus
  Solitary nucleus
  The solitary tract and nucleus are structures in the brainstem that carry and receive visceral sensation and taste from the facial , glossopharyngeal and vagus cranial nerves.-Anatomy:...
  
  : Taste from the posterior one-third of the tongue and information from carotid baroreceptors
  Baroreceptor
  Baroreceptors are sensors located in the blood vessels of several mammals. They are a type of mechanoreceptor that detects the pressure of blood flowing through them, and can send messages to the central nervous system to increase or decrease total peripheral resistance and cardiac output...
  
   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
  Nucleus ambiguus
  The nucleus ambiguus is a region of histologically disparate cells located just dorsal to the inferior olivary nucleus in the lateral portion of the upper medulla...
  
  : The lower motor neuron
  Lower motor neuron
  Lower motor neurons are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles...
  
  s for the stylopharyngeus muscle
• Inferior salivatory nucleus
  Inferior salivatory nucleus
  In the brain, the inferior salivatory nucleus is a cluster of neurons controlling the parasympathetic input to the parotid gland. It is one of the components of the glossopharyngeal nerve .-Location:...
  
  : Parasympathetic
  Parasympathetic nervous system
  The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
  
   input to the parotid
  Parotid gland
  The paired parotid glands are the largest of the salivary glands. They are each found wrapped around the mandibular ramus, and secrete saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches.-Location:The parotid glands...
  
   and mucous gland
  Mucous gland
  Mucous glands, found in several different parts of the body, typically stain lighter than serous glands during standard histological preparation...
  
  s.

Path

From the anterior portion of the medulla oblongata

Medulla oblongata

The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...

, the glossopharyngeal nerve passes laterally across or below the flocculus

Flocculus

The flocculus is a small lobe of the cerebellum at the posterior border of the middle cerebellar peduncle anterior to the biventer lobule....

, and leaves the skull through the central part of the jugular foramen

Jugular foramen

The jugular foramen is a large aperture in the base of the skull. It is located behind the carotid canal and is formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side....

. From the superior and inferior ganglia in jugular foramen it has its own sheath of dura mater

Dura mater

The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...

. The inferior ganglion on the inferior surface of petrous part of temporal is related with a triangular deppression into which the aqueduct of cochlea opens. On the inferior side, the glossopharyngeal nerve is lateral and anterior to the vagus nerve

Vagus nerve

The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...

 and accessory nerve

Accessory nerve

In anatomy, the accessory nerve is a nerve that controls specific muscles of the shoulder and neck. As part of it was formerly believed to originate in the brain, it is considered a cranial nerve...

.

In its passage through the jugular foramen (with X and XI), it passes between the internal jugular vein

Internal jugular vein

The two internal jugular veins collect the blood from the brain, the superficial parts of the face, and the neck.-Path:On both sides and at the base of the brain, the inferior petrosal sinus and the sigmoid sinus join to form the internal jugular vein...

 and internal carotid artery

Internal carotid artery

In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....

. It descends in front of the latter vessel, and beneath the styloid process

Styloid process (temporal)

The styloid process is a pointed piece of bone that extends down from the human skull, just below the ear.-Structure:The styloid process is a slender pointed piece of bone just below the ear...

 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

Hyoglossus

The Hyoglossus, thin and quadrilateral, arises from the side of the body and from the whole length of the greater cornu of the hyoid bone, and passes almost vertically upward to enter the side of the tongue, between the Styloglossus and Longitudinalis inferior....

 muscle, and is finally distributed to the palatine tonsil, the mucous membrane

Mucous membrane

The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

 of the fauces and base of the tongue

Tongue

The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...

, and the mucous glands of the mouth

Mouth

The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

Branches

• Tympanic
• Stylopharyngeal
• Tonsillar
• Nerve to carotid sinus
  Branch of glossopharyngeal nerve to carotid sinus
  The branch of the glossopharyngeal nerve to the carotid sinus and the carotid body is the nerve that runs downwards anterior to the internal carotid artery communicates with the vagus and sympathetic then divides in the angle of bifurcation of the common carotid artery to supply the carotid body...
  
  
• Branches to the posterior third of tongue
• Lingual branches
• A communicating branch to the Vagus nerve
  Vagus nerve
  The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
  
  

Note: The glossopharyneal nerve contributes in the formation of the pharyngeal plexus

Pharyngeal plexus

Pharyngeal plexus can refer to:* Pharyngeal plexus of vagus nerve* Pharyngeal plexus...

along with the vagus nerve.

Testing the glossopharyngeal nerve

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.