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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.
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.
Being rich in lipid, myelin appears white, hence the name given to the "white matter" of the CNS. Both CNS white matter tracts (e.g. the optic nerve, corticospinal tract and corpus callosum) and PNS nerves (e.g. the sciatic nerve and the auditory nerve, which also appear white) each comprise thousands to millions of axons, largely aligned in ...
Using structural MRI, quantitative assessment of a number of developmental processes can be carried out including defining growth patterns, [9] and characterizing the sequence of myelination. [10] These data complement evidence from Diffusion Tensor Imaging (DTI) studies that have been widely used to investigate the development of white matter.
The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. [1] There are more than one million neurons in the corticospinal tract, and they become myelinated usually in the first two years of life.
Myelination is a process by which axons are covered with a protective substance called myelin that drastically increases the signaling efficiency of the neuron. [7] The arcuate fasciculus is heavily myelinated in healthy adult brains. The density of this myelination has been found to predict the accuracy and speed to which one can comprehend ...
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]
OPCs continue to exist in both white and grey matter in the adult brain and maintain their population through self-renewal. [29] [30] White matter OPCs proliferate at higher rates and are best known for their contributions to adult myelinogenesis, while grey matter OPCs are slowly proliferative or quiescent and mostly remain in an immature state.