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Oligodendrocytes (from Greek meaning few-branching cells), or oligodendroglia, are a variety of neuroglia. Their main function is the myelination of nerve cells exclusively in the central nervous system of the higher vertebrates (in the peripheral nervous system the same function is carried out by Schwann cells). A single oligodendrocyte can extend to about a dozen axons, wrapping around approximately 1mm of each and forming the myelin sheath.
The nervous system (e.g., of humans) depends crucially on this sheath for insulation (decreased ion leakage and lower capacitance of the cell membrane), an overall increase in impulse speed (saltatory propagation of action potentials occurs in the PNS and the CNS at the nodes of Ranvier in between Schwann cells (of the PNS) and oligodendrocytes (of the CNS), and miniaturization (impulse speed of myelinated axons increases linearly with the axon diameter, whereas the impulse speed of unmyelinated cells increases only with the square root of the diameter).
Although they are part of the nervous system and very closely related to nerve cells, like all other glial cells the oligodendrocytes have a supporting role towards neurons and are probably not involved in signal propagation themselves.
Diseases that result in injury to the oligodendroglial cells include demyelinating diseases such as multiple sclerosis and dysmyelinating diseases called leukodystrophies. Oligodendroglia are also susceptible to infection by the JC virus, which causes progressive multifocal leukoencephalopathy (PML), a condition which specifically affects white matter, typically in immunocompromised patients. Tumors of oligodendroglia are called oligodendrogliomas.
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