Primary Neurulation

• Process: The neural plate thickens and bends to form neural folds that elevate, approach each other, fuse, and separate from the surface ectoderm, creating a hollow neural tube.

• Result: A hollow tube forms directly from the neural plate.

• Role in Brain Development: Primary neurulation forms the cranial neural tube, which develops into the brain and much of the spinal cord.

• Regions: Occurs in anterior regions including the majority of the brain.

Secondary Neurulation

• Process: Mesenchymal cells in the caudal eminence condense to form a solid medullary cord. This cord then cavitates (forms hollow spaces inside) and connects with the anterior hollow neural tube.

• Result: Hollowing of the initially solid cord forms the neural tube at the caudal (tail) end.

• Role in Brain Development: Secondary neurulation primarily contributes to the formation of the caudal spinal cord, not the brain.

Statement Review

• A: In primary neurulation, a hollow neural tube is formed → True

• B: In secondary neurulation, the neural tube arises from coalescence of mesenchymal cells into a solid cord → True

• C: The solid cord formed in secondary neurulation subsequently cavitates → True

Involvement in Brain Development

• The brain, part of the anterior neural tube, develops exclusively via primary neurulation.

• Secondary neurulation is limited to caudal portions of neural tube (tail and lower spinal cord regions).

Summary

Brain development in vertebrates involves only primary neurulation (A), where a hollow neural tube arises directly from the neural plate. Secondary neurulation (B and C) forms the posterior neural tube but is not involved in the formation of the brain.

Final Answer:
(3) only A

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