Which term correctly describes the paraxial mesoderm that forms the fifth pharyngeal arch?

Which term correctly describes the paraxial mesoderm that forms the fifth pharyngeal arch?

• A. Segmented (occipital somites)
• B. Unsegmented
• C. Neural crest-derived mesoderm
• D. Lateral plate mesoderm

Answer: (A)

The mesoderm that makes up the pharyngeal arches comes from paraxial mesoderm organized into somites. In the head and neck region, the portion that contributes to the arches is segmented into occipital somites. So the fifth pharyngeal arch is formed from this segmented paraxial mesoderm originating from occipital somites. This is why segmented (occipital somites) is the best description. The other possibilities miss the fact that this arch’s mesoderm is derived from a segmented, somite-forming region of the paraxial mesoderm, not from unsegmented paraxial mesoderm, lateral plate mesoderm, or neural crest–derived mesoderm.

The mesoderm that makes up the pharyngeal arches comes from paraxial mesoderm organized into somites. In the head and neck region, the portion that contributes to the arches is segmented into occipital somites. So the fifth pharyngeal arch is formed from this segmented paraxial mesoderm originating from occipital somites. This is why segmented (occipital somites) is the best description. The other possibilities miss the fact that this arch’s mesoderm is derived from a segmented, somite-forming region of the paraxial mesoderm, not from unsegmented paraxial mesoderm, lateral plate mesoderm, or neural crest–derived mesoderm.