What are the three streams from which neural crest cells migrate from the rhombencephalon to the pharyngeal arches?

• A. R1/2, R4, R6/7
• B. R2/3, R4, R5/6
• C. R1/3, R2/4, R6/7
• D. R1, R3, R5/7

Answer: (A)

Cranial neural crest cells migrate in streams defined by their rhombomere of origin as they populate the pharyngeal arches. The first stream comes from rhombomeres 1 and 2 and enters the first pharyngeal arch, shaping much of the facial skeleton. The second stream originates from rhombomere 4 and migrates into the second pharyngeal arch, contributing to structures derived from that arch. The third stream arises from rhombomeres 6 and 7 and moves into the third and fourth pharyngeal arches, forming the tissues of the later arches. This pattern aligns with how neural crest derivatives map to the arches and their nerves. Other proposed groupings don’t match these established migratory routes, so they don’t fit the correct organization.