The Glossopharyngeal Nerve and Vagus Nerve (Cranial Nerves IX and X) and Their Disorders

Since these two cranial nerves are intimately connected, they are described here together. The glossopharyngeal nerve has a sensory and motor component. The motor fibers arise from the nucleus ambiguous located in the lateral part of the medulla. Along with the vagus and accessory nerves, they leave the skull through the jugular foramen. They supply the stylopharyngeus muscle function function is to elevate the pharynx. Autonomic afferent fibers of the glossopharyngeal nerve arise from the inferior salivatory nucleus. The preganglionic fibers pass to the otic ganglion through the less superior petrosal nerve. and postganglionic fibers pass through the auriculotemporal branch of the fifth nerve to reach to reach the Parotid gland. The nuclei of the sensory fibers of the glossopharyngeal nerve are located in the petrous ganglion which lies within the petrous bone below the jugular foramen and also the superior ganglion, which is small. The exteroceptive fibers supply the faucial tonsils, posterior wall of the pharynx, part of the soft palate and taste sensations from the posterior third of the tongue.

The vagus : This is the longest among all the cranial nerves. The motor fibers arise from the nucleu ambiguus and supply all the muscles of the pharynx, soft palate and larynx, with the exception of tensor veli palati and stylopharyngeus. The parasympathetic fibers arise from the dorsal efferent nucleus and leave the medulla as preganglionic fibers of the craniosacral portion of the autonomous nervous system. These fibers terminate on ganglia close to the viscera which they supply by post-ganglionic fibers. The are parasympatahetic in function. Thus vagal stimulation products bradycardia, bronchial constriction, secretion of gastric and pancreatic juice and increased peristalsis. The sensory portion of the vagus has its nuclei in the jugular in ganglion and ganglion nodosum. The vagus carries sensations from the posterior aspect of the external auditory meat and adjective pinna and pain sensation from the duramater lining the posterior cranial fossa.

Testing : It is better to test the 9th and 10th nerve functions together as they are affected usually together. Inquire for symptoms like dysphagia, dysarthria, nasal regurgitation of fluids and hoarseness of voice. The motor part is tested by examining the uvula when the patient is made to open his mouth. The Uvula is usually in the midline. In unilateral vagal paralysis, the palatal arch is flattened and lowered ipsilaterally. On phonation, the uvula is deviated to the normal side.

The gag reflex or the pharyngeal reflex is elicited by applying a stimulus, such as a tongue balde or cotton to the psoterior pharyngeal wall or tonsillar region. If the reflex is present, there will be elevation and contraction of the pharyngeal musculature accompanied by retraction of the tongue. The afferent arch of this reflex is reserved by the glossopharyngeal while the efferent is through the vagus. This reflex is lost in either 9th or 10th nerve lesions. Test for general sensations over the posterior pharyngeal wall, soft palate and faucial tonsils, and taste over the posterior third of the tongue. These are impaired in glossopharyngeal paralysis.

Disorders of ninth and tenth nerve functions
Isolated involvement of either nerve is rare and usually they are involved together, often the eleventh and twelve nerves may also be affected. Glossopharyngeal neuralgia resembles trigeminal neuralgia, but it is much less common. It occurs as paroxysmal intense pain originating in the throat from the tonsillar fossa. It may be associated with bradycardia and in such cases it is called vegoglossopharyngeal neuralgia. A trial of phenytoin or carbamazepine is usually effective in relieving pain. Brain stem lesions like motor neuron disease, vascular lesions such as lateral medullary infarction or bulbar poliomyelitis can affect these nerves together resulting in bulbar palsy. Posterior fossa tumors and basal meningitis may involve these nerves outside the brain stem. Complete bilateral vagal paralysis is incompatible with life. Involvement of the recurrent laryngeal nerves, especially the left, occurs in thoracic lesions and this produces only hoarseness of voice without dysphagia.