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Neural Tube Closure: Closure Points

NEURO-V0WTVG

Mechanistically neural tube closure can be described as the bending, elevation and fusion of neural folds.

Neural Crest Formation during Neurulation. Digital image. Wikipedia.org. N.p., n.d. Web. 1 Apr. 2016. https://commons.wikimedia.org/wiki/File:Neural_Crest.png.

Neural tube closure is initiated at several points along the neural tube, at different developmental stages. In a mouse embryo, the tips of the neural ridges typically have met and fused at the midline of the hindbrain/cervical boundary first, and neural tube fusion proceeds both rostrally (toward the hindbrain) and caudally (toward the trunk).

Closure initiated from this point is named closure 1. Next, the neural ridges meet and fuse at the forebrain/midbrain boundary, initiating closure 2, which also proceeds bi-directionally from the contact point.

A third fusion initiation point begins at the rostral end of the neural plate. This closure 3 proceeds caudally and meets the rostrally directed wave of closure 2 to seal the anterior neuropore. The caudally directed closure 2 meets the rostrally directed closure 1 to seal the midbrain-hindbrain neuropore.

What is the MOST likely consequence of failure in closure 2?

A

Microcephaly is a neurodevelopmental disorder characterized by abnormally small brain size.

B

Exencephaly is a neurodevelopmental disorder where the brain is located outside the skull.

C

Megalencephaly is a neurodevelopmental disorder characterized by abnormally large brain size.

D

Spina bifida is a birth defect where there is incomplete closing of the backbone and membranes around the spinal cord.