Glossopharyngeal Nerve - Overview of Visceral Motor Component

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)