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Embryology · USMLE Step 1

USMLE Embryology: Neural Tube Development and Defects

Neural tube formation and closure timing paired with the neural tube defect that results when each step fails.

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What is the process called by which the neural plate folds into the neural tube?
Neurulation
What embryonic structure induces the overlying ectoderm to become neuroectoderm?
The notochord
In approximately what gestational week does neurulation begin?
Week 3
What flat structure of thickened neuroectoderm is the first visible sign of neural tube formation?
The neural plate
What paired elevations flank the neural groove as the neural plate invaginates?
The neural folds
The neural tube begins closing near the ____ region and proceeds in both cranial and caudal directions like a zipper.
cervical
On approximately what day of development does the anterior (rostral) neuropore close?
Day 25
On approximately what day of development does the posterior (caudal) neuropore close?
Day 27 to 28
Failure of closure of the anterior neuropore causes what neural tube defect?
Anencephaly
Failure of closure of the posterior neuropore causes what category of neural tube defect?
Spina bifida
In anencephaly, what happens to the forebrain tissue that is left exposed without covering neural tube?
It degenerates in utero
What maternal condition often accompanies anencephaly, due to the fetus's impaired swallowing reflex?
Polyhydramnios
What is the mildest form of spina bifida, in which the vertebral arch fails to close but no tissue herniates?
Spina bifida occulta
What cutaneous finding often overlies spina bifida occulta?
A tuft of hair or a skin dimple over the lower back
What term describes herniation of the meninges alone, without neural tissue, through a vertebral defect?
Meningocele

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