Question

Describe in detail the development of the neural tube, early brain and spinal cord development in vertebrates complete with relevant signaling systems.

Answer 1

Ectoderm give rise to neural crest and neural tube. Neural crest further lead to form the peripheral nervous system while neural tube leads to form brain and spinal cord. Neural tube is formed by the primary neurulation. In this process ectoderm divides and form neural tube, epidermis and neural crest cell.

This process forms and fold the neural tube first. Underlying mesoderm send signals to ectoderm to elongate. Cells of the neural plates divides in the antero-posterior direction. After this neural plate's bending forms a medial hinge point (MHP). This region attached with the notochord present beneath it. Dorso lateral hinge points (DLHP) also forms which later become wedge shaped. This leads to changement in the shape of cell. Colchicine inhibits this elongation, cytochalasin B stops the construction so that it can inhibit the wedge formation. Later on the neuroepithelial cells get enlarged and it leads to the accumulation of the regulatory protein at apical end of the cells. The hinges bend due to furrowing of neural tube. The embroy's surface ectoderm also get pushed by extrinsic force so that it further helps in bending. Later on the closure of neural tube takes place by the pairing of neural folds which get adhered simultaneously along the anterior posterior axis. It forms a shape of closed cylinder which get detached from surface ectoderm. To ensure the separation of neural tube from surface ectoderm secrete N cadherin (NCAM) . Various genes such as pax3 , openbrain, hedgehog are helpful in the formation of neural tube.

After primary neurulation secondary neurulation takes place which leads to the formation of mesenchyme cells which makes the central portion of the cord forms hollow spaces which later joins and form a single large cavity . The neural tube's lumen bulges out and constrict to form chambers of the brain and spinal cord.

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