Cerebral Cortex: Development


The ontogenic growth of the cerebral cortex is a complicated and finely harmonized process regulated by the interaction between genes and the environment. The cerebral cortex originates from the most anterior portion of the neural plate, a particular part of the embryonic ectoderm. The neural plate folds and closes to create the neural tube, From the cavity within the neural tube develops the ventricular system and, via the epithelial cells of its walls, which are the neurons and glia of the nervous system. The most anterior (from, or cranial) portion of the neural plate. The prosencephalon, which is apparent before neurulation begins, gives rise to the cerebral hemisphere and its later cortex.

Cortical neurons are produced within the ventricular zone, next to the ventricles. Initially, this zone contains progenitor cells, which divide to produce glial cells and neurons. The glial fibers developed in the first divisions of the progenitor cells are symmetrically located, crossing the thickness of the cortex from the ventricular zone to the outer, pial surface, and afford the scaffolding of the progenitor cells are symmetric, which duplicates the total number of progenitor cells at each mitotic cycle. Next, some progenitor cells start to divide asymmetrically, producing one post-mitotic cell that moves along the radial glial fibers, moving away from the ventricular zone, and one progenitor cell, which proceeds to separate until the end of development, when it changes into a glial cell or an ependymal cell. As the G1 phase of mitosis is elongated, in what is seen as selective cell cycle lengthening, the newly- born neurons migrate to more superficial layers of the cortex. The migrating quarterer cells become the pyramidal cells of the cerebral cortex. The development process is time dictated and controlled by hundreds of genes and epigenetic regulatory systems and mechanisms.

The layered structure of the fully-developed cerebral cortex is created during maturation. The first pyramidal neurons generated migrate out of the ventricular zone, together with reelin-producing Cajal-Retzius neurons, from the prelate. Next, a cohort of neurons relocating into the middle of the prelate divides that transient layer into the superficial marginal zone, that will become layer one of the mature neocortex, and the subplate, developing a middle layer named the cortical plate. These cells will make the deep layers of the mature cortex, layers five and six. Later born move radially into the cortical plate past the deep layers, neurons, and become the upper layers (tow to four). Thus, the layers of the cortex are generated in an inside-out order. The only exemption to this inside-out progression of neurogenesis transpires in the layer I of primates, in which, which is different from other mammals, whereby neurogenesis continues through the entire period of corticogenesis.

The map of functional cortical areas, which is comprised of the primary motor and visual cortex, originates from a protomap, which is regulated by molecular signals such as fibroblast growth factor FGF8 early in embryonic development. These signals control the size, shape, and location of cortical areas on the surface of the cortical primordium, in part by controlling gradients of transition factor expression, through a process described as cortical patterning. Examples of such transcription factors comprise the genes EMX2 and PAX6. The rapid expansion of the cortical surface area is regulated by the amount of self-renewal of radial glial cells and is somewhat governed by FGF and Notch genes. During the period of cortical neurogenesis and layer formation, many higher mammals begin the process of gyrification, which generates the characteristic fold of the cerebral cortex. Gyrification is regulated by the gene Trnp1 and by FGF and SHH signaling.

 

Cortical Layers of The Cerebral Cortex

Cerebral Cortex Function: Connections, Sensory, Motor,Association