Index
It is afferent to the tongue and the pharynx, hence its name, and efferent for the stylopharyngeus and the parotid gland.
The glossopharyngeal nerve, CN IX, is the ninth paired cranial nerve.
This provides:
- Sensation in all forms, including the taste of the posterior 1/3 of the tongue. (Remember that the facial nerve is responsible for taste 2/3 above).
- Somatosensory (i.e., touch, pain, and temperature) of the soft palate mucosa and the upper pharynx mucosa.
- A parasympathetic portion of CN IX Innervates the parotid salivary glands to help moisten and form a cohesive bolus.
Embryologically, the glossopharyngeal nerve is associated with the derivatives of the third pharyngeal arch.
- Sensory: Innervates the oropharynx, the carotid body, breast, 1/3 posterior of the tongue, the middle ear cavity, and the eustachian tube.
- Sensory special: Provides flavor sensation 1/3 rear of the language.
- Parasympathetic: Provides parasympathetic innervation to the parotid gland.
- Motor: Innervates the stylopharyngeus muscle of the pharynx.
Anatomical course
It originates in the medulla oblongata of the brain. It emerges from the anterior side of the marrow, moving laterally in the posterior cranial fossa.
It comes out of the skull through the jugular foramen. At this point, the tympanic nerve arises. It has a mixed sensory and parasympathetic composition, showing the innervation of the stylopharyngeus muscle.
Immediately outside the jugular foramen are two ganglia (collections of nerve cell bodies). They are known as the upper and lower ganglia (or rock); They contain the cell bodies of the sensory fibers in the glossopharyngeal nerve.
It goes down the neck, anterolateral to the internal carotid artery. In the inferior margin of the stylopharyngeus, several branches arise to provide motor innervation of the muscle. It also gives rise to the carotid sinus nerve, which provides sensation to the carotid sinus and the body.
Enter the pharynx as it passes between the upper and middle pharyngeal constrictors. The pharynx is divided into several branches: lingual, amygdala, and pharyngeal.
Sensory functions
It provides sensory innervation with various structures in the head and neck.
The tympanic nerve arises when it passes through the jugular foramen. Penetrates the temporal bone and enters the middle ear cavity. Here, it forms the tympanic plexus, a network of nerves that provide:
- The sensory innervation of the middle ear.
- The inner surface of the tympanic membrane.
- The eustachian tube.
At the stylopharyngeal level, the carotid sinus nerve arises. It goes down the neck to innervate both the carotid sinus and the carotid body, providing blood pressure and oxygen saturation information.
Ends dividing into several sensory branches:
- The pharyngeal branch is combined with the vagus nerve fibers to form the pharyngeal plexus. Innervates the mucosa of the oropharynx.
- Lingual branch: provides the posterior third of the tongue with general and taste sensation.
- Amygdala branch: forms a network of nerves, known as the amygdala plexus, which innervates the palatine tonsils.
Special sensory
It provides gustatory sensation to the posterior 1/3 of the tongue through its lingual branch ( Note: it should not be confused with the lingual nerve).
Engine functions
The glossopharyngeal nerve innervates the stylopharyngeus muscle of the pharynx. This muscle shortens and widens the pharynx and elevates the larynx during swallowing.
Parasympathetic functions
It provides parasympathetic innervation to the parotid gland. These fibers originate in the inferior salivary nucleus of CN IX. These fibers travel with the tympanic nerve to the middle ear. From the ear, the fibers continue as the lesser petrosal nerve before the synapse in the otic ganglion.
The fibers then hitchhike in the auriculotemporal nerve to the parotid gland, where they have a secretomotor effect.
Remember: Although the facial nerve divides into its five terminal branches in the parotid gland, the glossopharyngeal nerve supplies the gland.
Clinical relevance
It supplies sensory innervation to the oropharynx and transports the afferent information to the gag reflex. When a foreign object touches the back of the mouth, this stimulates the CNIX, beginning the reflex. The efferent nerve in this process is the vagus nerve, CNX.
An absent gag reflex means damage to the glossopharyngeal nerve.
