In the central nervous system (CNS), oligoden¬drocytes share a similar function with

Oligodendrocytes in the central nervous system (CNS) share a similar function with Schwann cells in the peripheral nervous system-synthesis of myelin. Oli­godendrocytes are small, round, lymphocyte-size cells that produce and maintain CNS myelin, which is primarily located in the white matter. Certain diseases, such as progressive multifocal leukoencephalopathy, caused by a papovavirus, specifically attack oligoden­drocytes and produce demyelination. Oligodendrogli­omas are malignant tumors that are derived from oligo­dendrocytes. However, unlike Schwann cells, oligodendrocytes contribute segments of myelin sheaths to more than one axon. Gemistocytes are reactive astrocytes that have an eosinophilic cytoplasm. They are commonly seen along the periphery of cerebral infarctions. Some astro­cytomas have a gemistocytic appearance. Astrocytes provide the structural framework for the neurons and are analogous to the fibroblasts in connec­tive tissue. However, scarring in the brain is not associ­ated with collagen synthesis but with filling in the defect with the cellular processes of astrocytes. A cere­bral abscess is the only example of CNS repair with collagen, which is derived from the blood vessels. Microglial cells are derived from monocytes. They are the phagocytic cell of the CNS. Ependymal cells line the ventricles of the brain and the spinal canal. They do not produce CSF nor are they responsible for reabsorption of CSF, a function relegated to arachnoid cells.