Directed Neurological Examination Cranial Nerve Ix

The functions of the glossopharyngeal nerve overlap with those of other cranial nerves, making it difficult to test in isolation.

Motor. The sole skeletal muscle innervation of cranial nerve IX is the stylopharyngeus, which aids in elevation of the pharynx. The oral cavity should be inspected visually at rest to ascertain whether asymmetrical lowering of the pharynx is present. The pharynx is elevated also by the palatopharyngeus and salpingopharyngeus muscles, both of which derive their nerve supply from the vagus nerve. Lesions of the glossopharyngeal nerve therefore may not produce any noticeable clinical motor effect.

Autonomic. The activity of parotid gland salivary secretion through Stensen's duct reflects autonomic functioning of the glossopharyngeal nerve. The duct is located on the inside of the cheek opposite the crown of the second upper molar tooth. Secretion from the parotid glands should be symmetrical, although the amount of saliva normally produced may vary. This quantity may be tested by having the patient suck on a lemon wedge, or by injecting pilocarpine intravenously, and then assessing saliva volume from the duct. Reduced volume of one side suggests glossopharyngeal autonomic dysfunction on that side. Saliva volume measurements for this purpose are impractical and are virtually never done.

Sensory. The sensory function of the glossopharyngeal nerve most accessible to testing is general visceral sensation (tactile, pain, temperature) of the posterior and lateral aspects of the pharynx, and the posterior third of the tongue and the tonsils. Testing is done by touching the soft tip of a cotton applicator to either side of these areas and asking the patient about asymmetry of sensation. Tactile sensation in these areas also serves to trigger the gag, or pharyngeal, reflex. Testing taste sensation of the posterior third of the tongue cannot be done reliably in the clinic. Testing may be accomplished in a laboratory setting by stimulating this area of the tongue with an electrical current.

Reflexes. The gag, or pharyngeal, reflex is centered in the medulla and consists of the reflexive motor response of pharyngeal elevation and constriction with tongue retraction in response to sensory stimulation of the pharyngeal wall, posterior tongue, tonsils, or faucial pillars. This reflex is examined by touching the posterior pharynx with the soft tip of a cotton applicator and visually inspecting for

elevation of the pharynx. Both sides of the pharynx should be examined for both the afferent and efferent limbs of the reflex by touching one side first and then the other, while watching for symmetry of pharyngeal movement. The normal reflex response varies, and it may be reduced in the elderly or in smokers. Asymmetry of the reflex is the feature most indicative of pathology.

CRANIAL NERVE X

Motor innervations of the vagus nerve to the soft palate, larynx, and pharynx are readily available for testing.

Motor. Inspection of the palate on phonation shows deviation of the uvula to the intact side with a unilateral vagus nerve lesion. The unaffected muscles contract normally, drawing the uvula upward and pulling it laterally away from the side of the lesion. A lesion involving the branches of the vagus nerve to the larynx produces vocal cord paresis on that side. The affected cord lies between abduction and adduction. The patient may demonstrate a mild hoarseness, or speech may be unaffected because of compensatory movement of the intact vocal cord. A lesion affecting innervation to the palate produces speech with a nasal quality. This quality is due to inability to close the nasal passage by palate elevation during phonation, allowing air to escape into and resonate within the nasal cavity. The patient may also have dysphagia due to involvement of pharyngeal muscles, with liquids escaping into the nasal cavity during swallow. Vocal cord function can be assessed by listening to the patient's speech to detect a hoarse or breathy voice with reduced volume. Cord function is best examined by visualization using indirect or direct laryngoscopy. Videostroboscopy recording using the fiberoptic direct laryngoscope may also be helpful to assess vocal cord movement.

Sensory. Sensory testing of the vagus nerve cannot be reliably accomplished in the routine neurological examination. Regions of the body that have vagus sensory innervation are either inaccessible or also have sensory input from the fifth and ninth cranial nerves.

Autonomic. The carotid sinus baroreceptors are innervated by the carotid sinus nerve branch of the glossopharyngeal nerve. Their stimulation results in heart rate reduction mediated by the vagus nerve. Testing the integrity of these fibers by carotid artery massage is not only impractical and unreliable but also is potentially dangerous. This maneuver may produce asystole or ventricular arrhythmia and should be done only where resuscitative means are immediately available, and not as part of a neurological examination. The vagus nerve is the efferent limb also of the oculocardiac reflex, where heart rate is decreased by pressure upon the eyeball. The afferent impulses for this reflex are conveyed by the trigeminal nerve. The heart rate may slow slightly when the reflex is intact. Heart rate is influenced by numerous factors, however, and this reflex is not a reliable test for vagus nerve integrity. Testing of autonomic functions related to the vagus nerve is addressed in the chapter on the autonomic nervous system.

Reflexes. The vagus nerve participates in several reflexes, including coughing, swallowing, sneezing, yawning, and hiccups, but only the gag reflex lends itself to routine testing in the neurological exam. The gag reflex involves afferent fibers provided by the glossopharyngeal nerve (and, in some people, also the vagus nerve) and motor efferents to the pharynx, soft palate, and tongue from the vagus. The reflex is elicited by tactile stimulation of the walls of the pharynx or the posterior tongue. The reflex consists of symmetrical contraction and elevation of the pharynx and retraction of the tongue. This process is described earlier in the section on reflex testing of the glossopharyngeal nerve.

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