Neural Tube Flashcards
What are three types of neurulation?
Primary, secondary, junctional
What is Primary Neurulation?
The primary neural tube forms by folding and bending of the neural plate, a thickened epithelial sheet induced by the underlying notochord. High levels of cell proliferation are necessary to drive the edges of the sheet up (the neural folds), leaving the center of the sheet down (the neural groove).
When does Primary Neurulation occur?
Starts on day 20 post- fertilization
Cranial closure is completed on day 24
Continues in the claudal region forming progressively lower levels of the neuraxis until day 26
Where does Primary Neurulation occur?
The primary neural tube closes first at the BOUNDARY BETWEEN THE FUTURE HINDBRAIN AND CERVICAL SPINE. From here (site 1), the neural tube closes like a zipper bidirectionally up into the hindbrain and down the spine. Closure initiates separately at the rostral extremity of the forebrain (sites 2/3), and zipping proceeds backwards to meet the wave of forward closure from the hindbrain.
What is Secondary Neurulation?
Formation of the secondary neural tube.
The tailbud is formed from the remnants of Henson’s node and the primitive streak. It generates all three germ layers of the caudal-most part of the embryo. The most dorsal of the condensations (the medullary cord) undergoes canalization, converting the solid neural precursor into a hollow epithelial lined tube. This is achieved by cellular rearrangements known as a mesenchymal to epithelial transition (MET).
When does Secondary Neurulation occur?
Days 28-48 post-fertilization.
Where does Secondary Neurulation occur?
The secondary neural tube arises in the tailbud, a pluripotent, mesenchymal population. The cell core of the tailbud progressively reorganizes into longitudinal cell condensations.
types of neural tube defects
- Exencephaly/anencephaly
- Craniorachischisis
- Spina bifida: meningocele and myelomeningocele
- Tethered cord
