Regarding closure of the neural tube in humans, which of the following correctly pairs the neuropore with its time of closure?
- A Anterior neuropore on day 25, posterior neuropore on day 27 ✓
- B Anterior neuropore on day 18, posterior neuropore on day 20
- C Anterior neuropore on day 27, posterior neuropore on day 25
- D Both neuropores close simultaneously on day 28
Correct answer: A. Anterior neuropore on day 25, posterior neuropore on day 27
Explanation
Neurulation begins with formation of the neural plate around day 18. Fusion starts in the cervical region and proceeds bidirectionally, leaving the cranial and caudal neuropores open temporarily. The anterior neuropore closes around day 25 and the posterior neuropore around day 27, so failure of anterior closure produces anencephaly while caudal failure produces spina bifida with myeloschisis. Both are closed well before day 28.
Reference: Langman's Medical Embryology, 14th ed.
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