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The studies on a rat optic nerve revealed that 15 days post-natal is when an increase in myelination is observed. Before this time period, most of the axons, roughly about 70%, are not myelinated. At this time, [35S] Sulfate was incorporated into sulfatide and the activity of cerebroside, sulfotransferase reached a peak in enzyme activity. This ...
The process of generating myelin is called myelination or myelinogenesis. In the CNS, oligodendrocyte progenitor cells (OPCs) differentiate into mature oligodendrocytes, which form myelin. In humans, myelination begins early in the 3rd trimester, [ 11 ] although only little myelin is present in either the CNS or the PNS at the time of birth.
a late-myelinating zone, which he called “association”. [3] The last area of the human cerebral cortex to myelinate is the Dorsolateral Prefrontal cortex. (Flechsig #45, Brodmann areas 9 & 46). This region continues to develop in adolescence and adulthood it is related to executive function and working memory.
The formation of the neural tube from the ectoderm is called neurulation. The ventral part of the neural tube is called the basal plate; the dorsal part is called the alar plate. The hollow interior is called the neural canal. By the end of the fourth week of gestation, the open ends of the neural tube, called the neuropores, close off. [5]
The maturation of myelination in intracortical layers coincides with critical period closure in mice, which has led to further research on the role of myelination on critical period duration. [ 37 ] Myelin is known to bind many different axonal growth inhibitors that prevent plasticity seen in critical periods. [ 38 ]
Pruning starts near the time of birth and continues into the late-20s. [2] During the pruning of a synapse, both the axon and the dendrite decay and die off. Synaptic pruning was traditionally considered to be complete by the time of sexual maturation, but MRI studies have discounted this idea. [3]
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 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]