Which cell population primarily contributes to the ectomesenchymal core of pharyngeal arches?

• A. Neural Crest Cells
• B. Paraxial Mesoderm
• C. Endodermal Cells
• D. Epithelial Cells

Answer: (A)

The main idea is that the ectomesenchymal core of the pharyngeal arches comes from cranial neural crest cells. These cells undergo an epithelial-to-mesenchymal transition and migrate into each arch, populating the internal core with mesenchyme that later differentiates into the facial skeleton, including cartilage and bone. This neural crest–derived mesenchyme is the distinctive source of the arch core, which is why it forms the skeletal elements of the face and surrounding structures. Paraxial mesoderm mainly contributes to muscle and some other tissues, not the primary ectomesenchymal core of the arches. Endodermal cells line the pharyngeal pouches, and epithelial cells line surfaces, but neither forms the core mesenchyme. So the neural crest cells are the population that primarily contributes to the ectomesenchymal core.