DrVirgo
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A physician is performing a cranial nerve examination on a patient. While testing the gag reflex, it is noted that when the right side of the pharyngeal mucosa is touched, the patient's uvula deviates to the right. When the left side of the pharyngeal mucosa is touched, the patient does not gag. Which of the following is the most likely location of his lesion?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
A. Left glossopharyngeal nerve and left vagus nerve
B. Left glossopharyngeal nerve only
C. Left vagus nerve only
D. Right glossopharyngeal nerve and right vagus nerve
E. Right glossopharyngeal nerve only
F. Right vagus nerve only
Please explain the answer; I'll post later.
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| Doc2378
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A.
Stimulating the right side -> right glossopharyngeal nerve (sensory) -> Uvula goes up on right but not left (lesion in left Vagus)
Stimulating on left side -> nothing happens (lesion in sensory limb of gag reflex on left side aka Left Glossopharyngeal n.)
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| DrVirgo
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You are right.
Can you please tell me the normal Gag Reflex. What happens when you stimulate the Left side versus when you stimulate the Right side.
Also: CN IX is responsible for moving the uvula to the same side, so lesion would result on uvula deviation to the contralateral side. Is that correct?
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| Doc2378
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Gag Reflex (the way I understand it) requires a sensory component, which is provided by Glossophayngeal nerve (nerve IX) and a motor component , provided by Vagus (cranial nerve X)
Stimulation of pharyngeal mucosa on one side -> stimulates the IXth nerve of that side -> efferent motor output is bilateral through right and left vagus -> Each sided vagus 'lifts' the uvula on its side and the cricopharyngeus m. contracts -> Gagging
Lesion of the IXth nerve would destroy the sensory afferent limb from that side
Lesion of Xth nerve would disrupt the efferent motor limb to that side, but since the efferent response is bilateral -> the intact Xth nerve would 'lift' the uvula on its side and thus the uvula appears to move 'away' from the side of lesion...
Hopefully this helps...
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Courage does not always ROAR. Sometimes courage is the quiet voice at the end of the day saying, "I will try again tomorrow" - Mary Anne Radmacher
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