Netter's Atlas of Neuroscience E-Book by Unknown

Author:Unknown
Language: eng
Format: epub
Publisher: Elsevier
Published: 2016-08-10T00:00:00+00:00

11.27 Glossopharyngeal Nerve (IX)

CN IX is a mixed nerve with motor, parasympathetic, and sensory components. Motor fibers from the nucleus ambiguus supply the stylopharyngeus muscle and may assist in the innervation of pharyngeal muscles for swallowing. Preganglionic parasympathetic axons from the inferior salivatory nucleus travel with CN IX to the otic ganglion, whose neurons innervate the parotid and mucous glands. Special sensory axons from the petrosal (inferior) ganglion carry information from taste buds on the posterior one third of the tongue (including numerous taste buds in the vallate papillae) and part of the soft palate. These axons terminate in the rostral portion of nucleus solitarius. Axons from additional primary sensory neurons in the inferior ganglion also carry general sensation from the posterior one third of the tongue and from the pharynx, the fauces, the tonsils, the tympanic cavity, the eustachian tube, and the mastoid cells. The central axon branches terminate in the descending (spinal) nucleus of CN V. The general sensory fibers from the pharynx provide the afferent limb of the gag reflex. Additional primary sensory neurons innervate the carotid body (chemoreception of carbon dioxide) and the carotid sinus (baroceptors) and convey their central axons to the caudal nucleus solitarius (solitary tract nucleus). Primary sensory neurons in the superior ganglion innervate a small region behind the ear and convey general sensation into the descending nucleus of CN V.

Clinical Point

The glossopharyngeal nerve can be affected by brief, excruciating paroxysms of pain (glossopharyngeal neuralgia) similar to those experienced in trigeminal neuralgia. The pain originates in the throat (tonsillar fossa) or sometimes the jaw and radiates to the ear. Some patients experience pain in the tongue, face, or jaw. The triggering activity is usually swallowing, coughing, sneezing, or yawning. If the irritative process activates glossopharyngeal afferents associated with brain stem vasomotor responses, the patient may experience bradycardia and syncope. The treatment of glossopharyngeal neuralgia is similar to treatment of trigeminal neuralgia. Successful treatment also has occurred surgically through decompression of a tortuous aberrant vessel.

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