gag reflex

(06) A 12-year old boy has a very active gag reflex when throat cultures are attempted. The EFFERENT limb of this reflex is carried in what cranial nerve? (please select the best answer)   

Choices

•  Trigeminal
•  Vagus
•  Glossopharyngeal
•  Facial

• Explanation

  Correct Answer: 
  Vagus (efferent)
  Take-Home Message: 
  The gag reflex results from sensory innervation through the glossopharygeal nerve (afferent limb) and motor innervation through the vagus nerve (efferent limb).
  Explanation of Correct Answer: 
  The soft palate and surrounding regions of the oropharynx are richly supplied with nerve endings, which carry sensory signals to the spinal cord by the glossopharyngeal nerve (afferent limb). Even light tough applied to these regions may elicit a strong gag reflex in some people. The efferent limb of this reflex is carried by the vagus nerve, which supplies the pharyngeal constrictors, levator veli palatini, palatoglossus, palatopharyngeus and the laryngeal muscles.
  Explanation of Incorrect Answers: 
  The glossopharyngeal nerve carries afferent fibers for the gag reflex, but not efferent fibers. The only muscle that receives motor innervation from the glossopharyngeal is the stylopharyngeus muscle, which does not play a role in the gag reflex.
  The trigeminal nerve is the major sensory nerve of the face and supplies motor fibers to the muscles of mastication, but not the muscles involved in the gag reflex.
  The facial nerve is the major motor nerve of the muscles of facial expression, as well as stylohyoid, stapedius and posterior belly of digastric, none of which are involved in the gag reflex
  Clinical Pearl: 
  The gag reflex can be impaired in patients after stroke and can lead to increased risk of aspiration pneumonia.
  For more information on this topic, please click on the following link(s): 
  (While these web sources have been vetted by our content experts, please use them with caution --- the peer-reviewed literature should be the ultimate source of medical information.) 
  http://library.med.utah.edu/neurologicexam/html/cranialnerve_anatomy.html#12 
  http://www.neuroanatomy.wisc.edu/virtualbrain/BrainStem/08CNX.html