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Education Module Learner Assessment May 07 Page My Learning Plan 1 January 07 2 February 07 3 March 07 4 April 07 5 May 07 6 June 07 7 July 07 III and V 8 August 07 V and VII 9 September 07 VII and IX November 11 07 December 12 07 CME Credit Expired 1 2 3 4 5 6 7 8 9 10 Editorial NeoPlus Overview Board 2007 10 October 07 Your Score You are evaluating an infant for poor feeding and drooling. You are unable to elicit a gag reflex by placing a gloved finger in the infant's mouth and stimulating the posterior tongue and pharyngeal wall. Of the following, the cranial nerves MOST important in the gag reflex are: IX and X X and XI You selected , the correct answer is . Do you want to add anything to your Learning Plan? (You must be an AAP member or PediaLink ® Learning Center Subscriber to use this feature.) Twelve pairs of cranial nerves (CNs), numbered I through XII from rostral to caudal, emerge from the base of the brain. They are called CNs because they emerge through fissures or foramina in the cranium, and because they are covered with sheaths derived from the cranial meninges. The gag reflex may be tested by inserting a gloved finger or tongue blade into the mouth, touching the posterior pharyngeal wall, and inspecting movement of the soft palate. The gag reflex, like all reflexes, requires an intact sensory and motor limb. The sensory limb of the gag reflex is mediated by the glossopharyngeal nerve, CN IX, which provides sensory fibers from the posterior part of the tongue and pharynx down to the level of the larynx. The motor limb of the gag reflex is mediated by the vagus nerve, CN X, which provides motor fibers to the palate elevator and pharyngeal constrictor muscles. Cranial nerves IX and X exit the brainstem closely together (Figure). Figure: Inferior view of brain and cranial nerves (CNs) involved in gag reflex. http://emb.aap.org/courseprodv2/Index.asp[4/6/2012 11:45:29 AM] Education Module Learner The lack of a gag reflex in a newborn infant may indicate abnormalities of the neural pathways involving CN IX and CN X. Cranial nerve III, the oculomotor nerve, provides motor fibers to the striated muscles of four of the six extraocular muscles (superior rectus, medial rectus, inferior rectus, and inferior oblique) and superior eyelid (levator palpebrae superioris). CN III does not play a role in the gag reflex. Cranial nerve V, the trigeminal nerve, has three branches: ophthalmic, maxillary, and mandibular. Motor fibers of the mandibular nerve supply the muscles of mastication: masseter, medial and lateral pterygoid, temporalis, mylohyoid, and anterior belly of digastric muscles. CN V does not play a role in the gag reflex. Cranial nerve VII, the facial nerve, supplies motor fibers to the face. CN VII exits the skull at the stylomastoid foramen and its main trunk forms the intraparotid nerve plexus. Five terminal motor branches of CN VII are located in the superficial fascia of the head and neck and supply the muscles of facial expression. The five branches of CN VII are the temporal, zygomatic, buccal, marginal mandibular, and cervical nerves. CN VII does not play a role in the gag reflex. Cranial nerve XI, the accessory nerve, is unique because it originates from both the brainstem and spinal cord. The brainstem root of CN XI provides motor fibers to the voluntary muscles of the pharynx, larynx, and soft palate. The spinal root of CN XI provides motor fibers to the sternocleidomastoid muscle. CN XI does not play a role in the gag reflex. Do you want to add anything to your Learning Plan? (You must be an AAP member or PediaLink ® Learning Center Subscriber to use this feature.) References: Fletcher MA. Neuromotor evaluation. In: Fletcher MA, ed. Physical Diagnosis in Neonatology. 1st ed. Philadelphia, Pa: Lippincott-Raven; 1998:453-462 http://emb.aap.org/courseprodv2/Index.asp[4/6/2012 11:45:29 AM] Education Module Learner Moore KL, Dalley AF. Neck. In: Moore KL, Dalley AF, eds. Clinically Oriented Anatomy. 5th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2006:1046-1121 Moore KL, Dalley AF. Summary of cranial nerves. In: Moore KL, Dalley AF, eds. Clinically Oriented Anatomy. 5th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2006:1124-1155 Tortora GJ. Cranial nerves. In: Tortora GJ, ed. Principles of Human Anatomy. 10th ed. Hoboken, NJ: John Wiley & Sons; 2005:610-623 Volpe JJ. Neurological examination: normal and abnormal features. In: Volpe JJ, ed. Neurology of the Newborn. 4th ed. Philadelphia, Pa: WB Saunders; 2001:10333 American Board of Pediatrics Content Specification(s): Understand the functions of the cranial nerves Know the neuroanatomic basis and methods of testing cranial nerve function in the newborn infant Recognize the features of cranial nerve palsies http://emb.aap.org/courseprodv2/Index.asp[4/6/2012 11:45:29 AM]