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Colour Coding
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Models: Central Nervous System | Cardiovasular | Gastrointestinal Tract |
6mm Pig Embryo - approximately Human day 32 (Carnegie Stage 13/14 embryo)
Central Nervous System
The central nervous system develops from the neural plate, a structure which appears on day 18. It is an ectodermal structure, extending along the surface of the embryo for much of its length. During the middle of the fourth week, an indentation the neural groove forms down the midline of the plate. This continues to deepen until the neural folds reach the 4th somite level, at which points the folds of the neural plate begin to fuse, forming the neural tube. The neural tube forms the eventual brain and spinal cord.
Simultaneously continuing during Week 4 is growth of the neural tube rostrally as 3 dilations:
These 3 vesicles of the neural tube are called the primary brain vesicles. The cavity within the tube forms the 4 ventricles of the brain and the central canal of the spinal cord. Later, these 3 vesicles split into 5, with each forming different areas of the central nervous system.
While the neural groove descends, the embryo grows and undergoes a series of folding processes. Although the embryo and amnion grow, the yolk sac does not grow, causing the embryo to fold laterally, caudally and cranially around the yolk sac. This folding process bends the neural tube, forming 2 noticeable flexures in the Stage 13/14 embryo.
Notochord
The notochord is a transient structure that begins to forms on day 20 underneath the ectoderm, from proliferating mesoderm, extending from the primitive node to the buccopharyngeal membrane. Initially forming as a hollow tube the notochordal process the structure fuses with the underlying endoderm and flattens out, forming the notochordal plate. Between days 22-24, it detaches from the endoderm, returning to its mesodermal space, and forms a solid cylinder the notochord. Research has shown that the notochord is the signaling site for differentiation of structures, including the floorplate of the spinal cord.
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