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This organization demands a tight developmental control and the formation of a variety of specialized zones of contact between different areas of the myelinating cell membrane. Each node of Ranvier is flanked by paranodal regions where helicoidally wrapped glial loops are attached to the axonal membrane by a septate-like junction.
Myelin is formed by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system.Therefore, the first stage of myelinogenesis is often defined as the differentiation of oligodendrocyte progenitor cells (OPCs) or Schwann cell progenitors into their mature counterparts, [4] followed by myelin formation around axons.
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.
Subventricular zone OPCs are activated and then migrate away from germinal [15] zones to populate both developing white and gray matter, where they differentiate and mature into myelin-forming oligodendrocytes. [11] [16] However, it is not clear whether all oligodendrocyte progenitors undergo this sequence of events. [17]
Following terminal differentiation in vivo, mature oligodendrocytes wrap around and myelinate axons. In vitro , oligodendrocytes create an extensive network of myelin-like sheets. The process of differentiation can be observed both through morphological changes and cell surface markers specific to the discrete stage of differentiation, though ...
White matter is the tissue through which messages pass between different areas of grey matter within the central nervous system. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation.
In order to compensate for the myelination (increased capacitance), leading up to the calyx at the last node (the area between the myelin sheath) before the axon terminal contains a high density of Na + channels in order to allow a large influx (inward flow) of sodium to trigger the voltage-gated calcium channels to open in the presynaptic ...
A myelinoid or myelin organoid is a three dimensional in vitro cultured model derived from human pluripotent stem cells (hPSCs) that represents various brain regions, the spinal cord or the peripheral nervous system in early fetal human development.