Glossopharyngeal Nerve - Overview of General Sensory Component

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.