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III and V
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V and VII
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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
.
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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.
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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
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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
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