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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.
Axial fluid-attenuated inversion recovery MRI image demonstrating tumor-related infiltration involving lenticular nuclei (Arrow). Axial fluid-attenuated inversion recovery MRI image demonstrating tumor-related infiltration involving both temporal lobes (Short arrow), and the substantia nigra (Long arrow).
MRI scans showing hyperintensities. A hyperintensity or T2 hyperintensity is an area of high intensity on types of magnetic resonance imaging (MRI) scans of the brain of a human or of another mammal that reflect lesions produced largely by demyelination and axonal loss.
Myelination is only prevalent in a few brain regions at birth and continues into adulthood. The entire process is not complete until about 25–30 years of age. [24] Myelination is an important component of intelligence, and white matter quantity may be positively correlated with IQ test results in children. [24]
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 ...
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.
The thinner myelin not only restores protection of the axon from degradation, [5] but also restores a faster conduction velocity. The conduction velocity, however, is not as strong as naturally myelinated axons and the Nodes of Ranvier are inclined to be wider which results in less coverage in the axon by myelin than what is natural. [6]
Diffusion imaging is an MRI method that produces in vivo magnetic resonance images of biological tissues sensitized with the local characteristics of molecular diffusion, generally water (but other moieties can also be investigated using MR spectroscopic approaches). [15] MRI can be made sensitive to the motion of molecules.