51. How does the embryo turn from gastrula into neurula? How is the neural tube formed? What is the embryonic origin of the nervous system in vertebrates?
The neurula stage is characterized by the appearing of the neural tube along the dorsal region of the embryo. The growing of mesoderm in that region induces the differentiation of ectodermal cells just above. These cells then differentiate forming the neural tube. Therefore, the origin of the nervous system is the ectoderm (the same germ layer that gives birth to the skin).
52. What is notochord? How is this structure formed?
Notochord is a rodlike structure that forms the supporting axis of the embryo and gives birth to the vertebral column in vertebrates. It is formed by differentiation of mesodermal cells.
53. What is coelom? To which structures do coeloms give birth? Are all animals coelomate?
Coeloms are cavities delimited by mesoderm. Coeloms originate the cavities where the internal organs of the body are located, like the pericardial cavity, the peritoneal cavity, and the pleural cavity. Besides coelomate animals, there are acoelomate animals, like platyhelminthes, and pseudocoelomate animals, like nematodes.
54. What is the germ layer from which the coeloms originate?
The coeloms are originated from mesoderm.
55. What are pleura, pericardium, and peritoneum?
Pleura are the membrane that covers the lungs and the inner wall of the chest; pericardium is the membrane that covers the heart; peritoneum is the membrane that covers most organs of the gastrointestinal tract and part of the abdominal cavity. All these membranes delimit coeloms (internal cavities).
56. After the neurula stage and from its ventral portion to the dorsal how can the morphology of the embryo be described?
In a schematic longitudinal section of the embryo after the neurula stage, the outermost layer of cells is the ectoderm. In the ventral region comes the archenteron tube formed of endodermal cells. In both sides of the embryo, coeloms delimited by mesoderm are present. In the central region above the archenteron and in the middle of the coeloms there is the notochord. In the dorsal region just above the notochord lies the neural tube.
57. What are somites?
Somites are differentiated portions of mesodermal tissue longitudinally distributed along the embryo. The somites originate the muscle tissue and portions of the connective tissues.
58. What are histogenesis and organogenesis?
Histogenesis is the process of tissue formation in the embryonic development. Organogenesis is the process of organ formation. Before histogenesis and organogenesis the primitive embryonic structures have been already formed: germ layers, neural tube, notochord, coeloms, somites.
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The neurula stage is characterized by the appearing of the neural tube along the dorsal region of the embryo. The growing of mesoderm in that region induces the differentiation of ectodermal cells just above. These cells then differentiate forming the neural tube. Therefore, the origin of the nervous system is the ectoderm (the same germ layer that gives birth to the skin).
52. What is notochord? How is this structure formed?
Notochord is a rodlike structure that forms the supporting axis of the embryo and gives birth to the vertebral column in vertebrates. It is formed by differentiation of mesodermal cells.
53. What is coelom? To which structures do coeloms give birth? Are all animals coelomate?
Coeloms are cavities delimited by mesoderm. Coeloms originate the cavities where the internal organs of the body are located, like the pericardial cavity, the peritoneal cavity, and the pleural cavity. Besides coelomate animals, there are acoelomate animals, like platyhelminthes, and pseudocoelomate animals, like nematodes.
54. What is the germ layer from which the coeloms originate?
The coeloms are originated from mesoderm.
55. What are pleura, pericardium, and peritoneum?
Pleura are the membrane that covers the lungs and the inner wall of the chest; pericardium is the membrane that covers the heart; peritoneum is the membrane that covers most organs of the gastrointestinal tract and part of the abdominal cavity. All these membranes delimit coeloms (internal cavities).
56. After the neurula stage and from its ventral portion to the dorsal how can the morphology of the embryo be described?
In a schematic longitudinal section of the embryo after the neurula stage, the outermost layer of cells is the ectoderm. In the ventral region comes the archenteron tube formed of endodermal cells. In both sides of the embryo, coeloms delimited by mesoderm are present. In the central region above the archenteron and in the middle of the coeloms there is the notochord. In the dorsal region just above the notochord lies the neural tube.
57. What are somites?
Somites are differentiated portions of mesodermal tissue longitudinally distributed along the embryo. The somites originate the muscle tissue and portions of the connective tissues.
58. What are histogenesis and organogenesis?
Histogenesis is the process of tissue formation in the embryonic development. Organogenesis is the process of organ formation. Before histogenesis and organogenesis the primitive embryonic structures have been already formed: germ layers, neural tube, notochord, coeloms, somites.
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