Neural tube defects (NTDs) are associated with folate deficiency. Which part of the neural tube is the LAST to close during normal neurulation, making it most vulnerable to defects?
- A Posterior neuropore (caudal end) ✓
- B Anterior neuropore (cranial end)
- C Cervical region
- D Mid-thoracic region
Explanation
Neural tube closure proceeds in a bidirectional, zipper-like fashion from the cervical region both cranially and caudally. The anterior (cranial) neuropore closes by day 25 of gestation; failure results in anencephaly. The posterior (caudal) neuropore closes by day 27-28 of gestation — it is the last to close. Failure of caudal neural tube closure results in spina bifida (myelomeningocele) at the lumbar level. Folate supplementation preconceptionally reduces NTD risk by ~70%. The caudal end's delayed closure explains why lumbosacral spina bifida is far more common than cranial defects.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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