Search results
Results From The WOW.Com Content Network
The central nervous system (CNS) is derived from the ectoderm—the outermost tissue layer of the embryo. In the third week of human embryonic development the neuroectoderm appears and forms the neural plate along the dorsal side of the embryo. The neural plate is the source of the majority of neurons and glial cells of the CNS.
This process is called zona hatching and it takes place on the sixth day of embryo development, immediately before the implantation process. The hatching of the human embryo is supported by proteases secreted by the cells of the blastocyst, which digest proteins of the zona pellucida, giving rise to a hole.
The remainder of the ectoderm gives rise to the epidermis. The ability of the mesoderm to convert the overlying ectoderm into neural tissue is called neural induction. In the early embryo, the neural plate folds outwards to form the neural groove. Beginning in the future neck region, the neural folds of this groove close to create the neural tube.
The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos. In the human being, only the first 60 days of development are covered; at that point, the term embryo is usually replaced with the term fetus.
The amount of time required to generate all the neurons of the CNS varies widely across mammals, and brain neurogenesis is not always complete by the time of birth. [3] For example, mice undergo cortical neurogenesis from about embryonic day (post-conceptional day) (E)11 to E17, and are born at about E19.5. [9]
Cortical white matter increases from childhood (~9 years) to adolescence (~14 years), most notably in the frontal and parietal cortices. [8] Cortical grey matter development peaks at ~12 years of age in the frontal and parietal cortices, and 14–16 years in the temporal lobes (with the superior temporal cortex being last to mature), peaking at about roughly the same age in both sexes ...
Embryonic age: Week nr 5. 4 weeks old. 29–35 days from fertilization. The embryo measures 8 mm (0.31 in) in length and weighs about 1 gram. [4] Optic vesicles and optic cups form the start of the developing eye. Nasal pits form. The brain divides into 5 vesicles, including the early telencephalon. Leg buds form and hands form as flat paddles ...
Brain of a human embryo in the sixth week of development. The brain develops in an intricately orchestrated sequence of stages. [71] It changes in shape from a simple swelling at the front of the nerve cord in the earliest embryonic stages, to a complex array of areas and connections.