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Old 10-31-2011
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Zygote Nerve to Stapedius, which pharyngeal arch!

A 2-year-old develops a middle ear infection. Examination shows the stapes, which is moved by the stapedius muscle, to be immobile. The nerve innervating this muscle is derived from which of the following structures?

A. Pharyngeal arch 4
B. Pharyngeal arch 1
C. Pharyngeal arch 5
D. Pharyngeal arch 3
E. Pharyngeal arch
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Old 10-31-2011
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A 2-year-old develops a middle ear infection. Examination shows the stapes, which is moved by the stapedius muscle, to be immobile. The nerve innervating this muscle is derived from which of the following structures?
A. Pharyngeal arch 4
B. Pharyngeal arch 1
C. Pharyngeal arch 5
D. Pharyngeal arch 3
E. Pharyngeal arch


(pharyngeal arch 2)
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Old 10-31-2011
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E.pharyngeal arch 2
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Old 11-01-2011
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The correct answer is E.
The patient has a middle-ear infection, which consists of the malleus, incus, and stapes. The stapedius muscle, which moves the stapes, is innervated by cranial nerve VII. Cranial nerve VII is derived from pharyngeal arch 2. The following are the other cranial nerves and their derivatives: Pharyngeal arch 1: Cranial nerves V2 and V3, Pharyngeal arch 3: Cranial arch IX, Pharyngeal arch 4: Cranial nerve X (superior laryngeal branch), Pharyngeal arch 5: none and Pharyngeal arch 6: Cranial nerve X (recurrent laryngeal branch).
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