On which days do the cranial end and the caudal end of the neural tube close, respectively?

• A. 23;25
• B. 24;26-28
• C. 25;27-29
• D. 26-28; 28-30

Answer: (B)

The process to focus on is when the neural tube closes along its ends during early development. The cranial neuropore closes first, around day 24 of gestation, and the caudal neuropore closes a bit later, roughly days 26 to 28. This sequencing means the correct pairing is 24 for the cranial end and 26–28 for the caudal end. Different texts may report slightly different exact days due to counting methods, but the important point is that the cranial end closes earlier than the caudal end. This timing explains why defects at the cranial end (like anencephaly) occur earlier in development, whereas caudal defects (such as certain spinal dysraphisms) arise a bit later.