The glossopharyngeal has branchial motor, visceral motor, general sensory visceral sensory and special sensory functions.
- Branchial motor to stylopharyngeus
- Visceral motor (parasympathetic) to the parotid gland
- General Sensory to the posterior 1/3rd of the tongue, tympanic cavity, pharyngotympanic tube, fauces, tonsils, nasopharynx and uvula.
- Special sensory to the taste receptors on the posterior 1/3rd of the tongue.
The nerve arises from four nuclei within the medulla – the nucleus ambiguus (branchial motor), inferior salivary nucleus (visceral motor), sensory nuclei of the trigeminal nerve (general sensory) and the nucleus of the solitary tract (special sensory).
It arises as a single stalk from the lateral medulla and passes to the jugular foramen. It passes through the anterior aspect of the foramen, which also includes the superior and inferior ganglia of the nerve. Upon exiting the skull, it lies between the internal jugular and carotid. It curves in front of the carotid and approaches the styloid process. It then follows behind this muscle to pierce the superior constrictor, passing further anterior to give off branches to the tonsils, fauces, pharynx and posterior third of the tongue.
There are several named branches of the glossopharyngeal:
The tympanic branch arises from the inferior ganglion in the jugular canal. It leaves the jugular canal via the inferior tympanic canaliculus, and forms the tympanic plexus on the medial wall of the tympanic cavity. As well as supplying sensation to the middle ear, the lesser petrosal nerve continues on from the tympanic plexus.
Lesser Petrosal Nerve
The lesser petrosal nerve is the continuation of the tympanic branch of the glossopharyngeal. As it leaves the tympanic cavity, it receives a connecting branch from the geniculate ganglion of the facial nerve. It emerges into the cranial cavity through a small hole near the greater petrosal foramen. Running anteriorly, it exits the cranium through the foramen ovale and enters the otic ganglion, where the preganglionic parasympathetic fibres synapse. Postganglionic fibres leave the otic ganglion and travel with the auriculotemporal nerve (branch of V3) to reach the parotid gland. Other postganglion fibres travel with the greater and lesser palatine nerves to reach the salivary glands of the palate.
The carotid branch arises just after the nerve emerges from the jugular foramen. It descends with the internal carotid to the carotid body, where it receives signals from baroreceptors and chemoreceptors.
These branches unite with the pharyngeal branch of the vagus nerve (X) as well as sympathetic fibres from the superior ganglion. It forms part of the plexus of nerves that supply the mucosa of the pharynx.
The muscular branch supplies the stylopharyngeus muscle.
A small tonsillar branch contributes to the sensory supply of the tonsil and fauces, together with the tonsillar branch of the maxillary nerve.
Lingual branches are the terminal parts of the nerve, and are distributed to the mucosa of the posterior 1/3rd of the tongue. Special sensory fibres from taste receptors in this region are also present.