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fireguy1 fireguy1
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12 years ago

I had this question posed to me by a young college student i guess she has to answer it for homework and I haven't had this stuff since medical school and couldnt help her and felt bad, so i told her i would find the answer and let her know can someone help me out, it is a pretty difficult question.

42. In humans, on about day 15 a thickened linear band of embryonic ectoderm appears in caudal midline of the bilaminar embryo called the primitive streak. Describe the significance of the primitive streak and the processes that occur subsequent to its appearance as they are encompassed by the term gastrulation (as it pertains to the human). Remember, at the end of gastrulation, the bilaminar embryo is a trilaminar embryo and has evolved all germ layers, a neural tube has formed and the embryo is prepared for organogenesis. Emphasize neural and mesodermal development. Be concise but inclusive.

And she said she is supposed to include terms like notochord and things like that. I know nobody will probably know everything but any little bit would help
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12 years ago
Cells migrate from the surface ectoderm through the primitive streak and primitive (a.k.a. Henson's) node to form the mesodermal cell layer. These cells form a continuous layer beneath the surface ectoderm as well as a midline rod-like structure called the notocord. Briefly, the ectoderm will become the skin and nervous system, the mesoderm will become the connective tissue, blood cells, skeletal muscle, and most internal organs, and the endoderm will become the respiratory and digestive tract. The notocord is an early version of the spinal cord. As gastrulation proceeds, the new mesodermal layer causes the "induction" of the overlying ectoderm to become the "neuroectoderm" or the "neural plate". The mesodermal induction of the neural plate is called primary neural induction. As more neural plate is formed, it begins to change shape in a process called neurulation, which is the transformation of the neural plate into a neural tube, Thus, the edges of the neural plate become "neural folds" that lift and bend towards the midline. Neural tube closure occurs initially in the region of the early hindbrain / upper spinal cord when the neural folds touch, make contact and fuse. The progression of the neural tube closure then continues in both directions, anteriorly and posteriorly.  The entire process of neurulation takes only about 5-6 days in humans.  

If she needs the whole process of embryonic CNS and PNS development, just let me know!
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