Question

What is neurulation?

Answer 1

Hint: The folding process in vertebrate embryos, which involves the transformation of the neural plate into the neural tube, is known as neurulation.

Complete answer:
The mechanism starts when the notochord signals the ectoderm germ layer above it to form the thick and flat neural plate, which causes the formation of the central nervous system (CNS). The neural plate folds in on itself to form the neural tube, which gradually differentiates into the spinal cord and brain, creating the central nervous system. Primary and secondary neurulation are two separate processes that shape different parts of the neural tube in different organisms.
The neural plate creases inward during primary neurulation until the edges meet and fuse. The cells of the neural plate become high-columnar as neurulation progresses after induction, and can be distinguished from the surrounding presumptive epithelial ectoderm using microscopy. The cells move laterally, away from the central axis, and take on the form of a truncated pyramid. Tubulin and actin in the apical portion of the cell are responsible for the pyramid form which constricts as they move.
The tube forms in secondary neurulation by hollowing out the interior of a solid precursor. The medullary cord is formed by the neural ectoderm and some cells from the endoderm during secondary neurulation. Condensation, separation, and cavity formation occur as the medullary cord condenses, divides, and then forms cavities. After that, the cavities converge to form a single tunnel. In most species, secondary neurulation occurs in the posterior region, but it is more prominent in birds.

Note:
Failure of neurulation, particularly failure of neural tube closure, is one of the most common and debilitating birth defects in humans. Anencephaly, or a lack of brain growth, occurs when the rostral end of the neural tube fails to close, and it is usually fatal.