Perspectives, Historical-landmarks in neurogenesis
The nervous system has the distinction of being the first organ primordium formed in the early embryo. After the fertilized egg has undergone its initial development i.e. cleavage and gastrulation (the latter resulting in the formation of the three germ layers: ecto-, meso-, and endo-derm), a pear-shaped ectodermal thickening appears on the dorsal side. This is the neural or medullary plate, the anlage of the nervous system. Its margins fold up, and the neural folds converge in the midline to form the hollow neural tube. From the beginning, its anterior part, the future brain, is broader than the posterior part, the spinal cord. The origin of the nervous system was described first by Carl Ernst von Baer, the founder of modern embryology, in his classical work Development History of Animals (1828) with the significant subtitle ‘Observation and Reflection’. Considering that he had only a hand lens and sharpened needles at his disposal—his work antedates the microtome and serial sections—his accurate description of the formation of most organs of Vertebrates was a monumental achievement.
KeywordsSchwann Cell Chick Embryo Growth Cone Spinal Ganglion Frog Embryo
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