History And Definitions

The glossopharyngeal and vagus nerves have been described since antiquity. Galen of Pergamus (131 to 201 AD) included them in his descriptions of neuroanatomy, grouping together cranial nerves IX, X, and XI as a single nerve. '1 Centuries later the anatomy of the glossopharyngeal and vagus nerves was elucidated in greater detail by the Prussian anatomist Samuel Thomas von Soemmering (1755-1830) in his treatise on the 12 cranial nerves. Although study of the glossopharyngeal nerve in isolation is impractical, the vagus nerve, with its numerous thoracic and abdominal visceral innervations, has long held the attention of physiologists, including the Russian Nobel Laureate Ivan Petrovich Pavlov (1849-1936), who, with E.O. Schumov-Simanovskaja, published in 1895 their prominent paper describing vagus nerve innervation for gastric secretion in dogs. The clinical consequences of pathology, particularly trauma and tumors, upon the glossopharyngeal or vagus nerves have been described by a number of authors who have attached their names to syndromes of the lower cranial nerves, beginning with John Hughlings Jackson in 1883.

Cranial nerves IX and X, the glossopharyngeal and vagus nerves, respectively, have their nuclei in the medulla, and they serve motor, sensory, and autonomic functions. Both nerves are formed by the joining of rootlets that emerge from the lateral medulla in a groove formed between the olive and the inferior cerebellar peduncle. The two nerves travel closely in their proximal courses, both exiting the skull at the jugular foramen, and consequently they are typically affected together by intracranial pathology. The name of the glossopharyngeal nerve refers in Latin to its targets of function, glosso referring to tongue and pharyngeal to the beginning of the alimentary canal. The vagus nerve is aptly named as well, with its numerous afferent and efferent functions in the head, neck, chest, and abdomen; vagus is a Latin adjective meaning wandering or roving.

Both the ninth and tenth nerves have components of branchial motor fibers (special visceral efferent) providing innervation of striated muscle, visceral motor fibers (general visceral efferent) to secretory glands, and both visceral and general sensory functions (general visceral and general somatic afferent). Additionally, the glossopharyngeal nerve has special afferent fibers receiving taste sensation from the posterior third of the tongue. Together the ninth and tenth cranial nerves provide sensory and motor innervation of the larynx and pharynx, including the afferent and efferent limbs of the gag reflex, and exteroceptive information for these structures, the tongue, the auditory meatus and tympanic membrane, and parts of the ear. The glossopharyngeal nerve also provides afferent input from the baroreceptors of the carotid sinus and the chemoreceptors of

the carotid body. The vagus nerve subserves esophageal peristalsis, heart rate and blood pressure modulation, gastric secretion, and bowel motility.

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