The glossopharyngeal nerve is the ninth of the twelve cranial nerves. The fibers consist of efferent motoric and parasympathetic fibers and afferent sensory fibers. In this article, the pathway of the efferent and afferent fibers will be discussed.
The word afferent means toward the centre, as in from a peripheral area of a limb to the central nervous system. The word efferent is the opposite of afferent, meaning away from the centre and toward the periphery; when the stimulus is carried to the peripheral area from the brain.
The pathway for the efferent fibers of the glossopharyngeal nerve is the following (from the initiation in the brain to the termination in the periphery):
- The nucleus ambiguous is situated behind the cuneate tubercle and the inferior salivary nucleus sits behind the medullary striae of the brainstem. They supply the efferent fibers and the parasympathetic fibers of the glossopharyngeal nerve respectively.
- They merge together into the main nerve bundle, synapse on the superior ganglion and then again on the inferior ganglion, which is situated just below it. This is the point of separation, because the postganglionic fibers divide off into a different branch.
- As the fibers pass from the superior ganglion to the inferior ganglion, they exit the skull through the jugular foramen.
- The parasympathetic fibers continue in the tympanic nerve and onto the tympanic plexus, situated in the tympanic cavity. It innervates the tympanic membrane.
- The fibers then continue in the lesser petrosal nerve and synapse in the otic ganglion.
- Postganglionic fibers run through the auriculotemporal nerve and they also branch directly off the ganglion into the parotid gland.
- Meanwhile, the efferent motoric fibers continue from the inferior ganglion as the glossopharyngeal nerve and where the nerve divides into its terminal branches, they continue to innervate the stylopharyngeus muscle.
The pathway for the afferent fibers of the glossopharyngeal nerve is the following (from the initiation in the periphery to the termination in the brain):
- The tympanic plexus supplies the auditory canal and the pharyngeal orifice.
- The fibers continue back through the tympanic nerve and synapse on the inferior ganglion of the glossopharyngeal nerve.
- Meanwhile the Pharyngeal Plexus supplies the Posterior Third of the Oral Cavity and consists of the following branches: pharyngeal, tonsillar and lingual.
- A further branch known as the carotid sinus branch also joins the main nerve bundle at the level of the plexus.
- The main bundle continues as the glossopharyngeal nerve and synapses on the inferior ganglion.
- There all branches merge as they pass postganglinicly through the skull at the jugular foramen and synapse on the superior ganglion.
- The fibers finally reach the brainstem and synapse on either the nucleus of the solitary tract or the trigeminal nucleus of the spinal tract.
nucleus ambiguous and inferior salivary nucleus -> superior and inferior ganglion -> tympanic plexus -> otic ganglion -> parotid gland and stylopharyngeus muscle
tympanic nerve and pharyngeal plexus -> inferior ganglion -> superior ganglion -> brainstem