Hypersensitivity of the facial nerve occurs in hypocalcemic tetany; spasm of the facial muscles is elicited by tapping in front of the ear (Chvostek sign) but this phenomenon is also seen in many normal individuals.
The Ninth, or Glossopharyngeal, Nerve
This nerve arises from the lateral surface of the medulla by a series of small roots that lie just rostral to those of the vagus nerve. The glossopharyngeal, vagus, and spinal accessory nerves leave the skull together through the jugular foramen and are then distributed peripherally. The ninth nerve is mainly sensory, with cell bodies in the inferior, or petrosal, ganglion (the central processes of which end in the nucleus solitarius) and the small superior ganglion (the central fibers of which enter the spinal trigeminal tract and nucleus). Within the nerve are afferent fibers from baroreceptors in the wall of the carotid sinus and from chemoreceptors in the carotid body. The baroreceptors are involved in the regulation of blood pressure, and chemoreceptors are responsible for the ventilatory responses to hypoxia. The somatic efferent fibers of the ninth nerve are derived from the nucleus ambiguus, and the visceral efferent (secretory) fibers, from the inferior salivatory nucleus. These fibers contribute in a limited way to the motor innervation of the striated musculature of the pharynx (mainly of the stylopharyngeus, which elevates the pharynx), the parotid gland, and the glands in the pharyngeal mucosa. A discussion of its role in swallowing is found in Chap. 25.
It is commonly stated that the glossopharyngeal nerve mediates sensory impulses from the faucial tonsils, posterior wall of the pharynx, and part of the soft palate as well as taste sensation from the posterior third of the tongue. However, an isolated lesion of the ninth cranial nerve is a rarity and therefore the effects are not fully known. In one personally observed case of bilateral surgical interruption of the ninth nerves, verified at autopsy, there had been no demonstrable loss of taste or other sensory or motor impairment. This suggests that the tenth nerve may be responsible for these functions, at least in some individuals. The role of the ninth nerve in the reflex control of blood pressure and ventilation has been alluded to earlier but referable clinical manifestations from damage of this cranial nerve are infrequent except perhaps for syncope as noted below.
One may occasionally observe glossopharyngeal palsy in conjunction with vagus and accessory nerve involvement because of a tumor in the posterior fossa or an aneurysm or intracranial dissection of the vertebral artery, or thrombosis of the sigmoid sinus or internal jugular vein. The nerves may be compressed as they pass through the jugular foramen. Hoarseness as a result of vocal cord paralysis, some difficulty in swallowing, deviation of the soft palate to the sound side, anesthesia of the posterior wall of the pharynx, and weakness of the upper trapezius and sternomastoid muscles make up the clinical picture (see Table 44-1, jugular foramen syndrome). On leaving the skull, the ninth, tenth, and eleventh nerves lie adjacent to the cervical internal carotid artery, where they can be damaged (presumably made ischemic) by a dissection of that vessel.
Glossopharyngeal Neuralgia (Also Discussed in Chap. 9)