A neonate presents with hoarseness, aphonia, and absence of laryngeal and pharyngeal muscles on the right side. Embryologically, the muscles of the pharynx and larynx are derived from which pharyngeal arches, and this defect suggests failure of which arch's mesoderm to differentiate?

• A First arch only; CN V innervation affected
• B Second arch; CN VII innervation affected
• C Third, fourth and sixth arches; CN IX, X innervation affected ✓
• D Fifth arch; CN XI innervation affected

Explanation

Pharyngeal muscles (stylopharyngeus, palatopharyngeus, salpingopharyngeus) derive from the third arch (CN IX) and fourth arch (CN X). The laryngeal muscles derive from the fourth and sixth pharyngeal arches, innervated by the superior laryngeal nerve (fourth arch) and recurrent laryngeal nerve (sixth arch), both branches of CN X (vagus). The second arch gives rise to facial expression muscles (CN VII). The first arch gives rise to muscles of mastication (CN V3). Defects in arch 3-4-6 mesoderm migration/differentiation lead to dysphagia, hoarseness, and aphonia.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.