Glial cells oligodendrocytes

Myelin A segmented laminated lipoprotein sheath formed by glial cells (oligodendrocytes and Schwann cells). It is wrapped round the axon and acts as a biological insulating material. 

The myelin sheath is one of the most abundant membrane structures in the vertebrate nervous system. It is produced by two types of glial cells, oligodendrocytes in the CNS and Schwann cells in the PNS. The myelin sheath is formed by the... 

Ependymal cells abut layers of astrocytes, which in turn envelop neurons, neurites and vascular components. In addition to neurons and glial cells, such as astrocytes and oligodendrocytes, the normal CNS parenchyma contains blood vessels and microglial cells, the resident macrophages of the CNS. 

Neurons and glial cells make up the bulk of the human nervous system. Glial cells come in several guises astrocytes, oligodendrocytes, microglia, and others. Glial cells serve a number of important functions in the human nervous system. 

Figure 14.4 Different types of glial cells. Astrocytes connect capillaries and neurones. Fibrous astrocytes, with less branching and more filamentous processes, occur mainly in white matter while protoplasmic astrocytes are located principally in the grey matter. Oligodendrocytes form the myelin sheath by wrapping themselves around axons. The connection between the myelin sheath and the oligodendrocyte is permanent and provides material for the myelin sheath. Microgliocytes (microglia) are the phagocytes of the nervous system. The ciliated ependymal cells line the cavities of the central nervous system.

The The brain parenchyma is composed of neurons supported by a framework of glial cells (astrocytes, oligodendrocytes, and ependyma), blood vessels, and microglia. The processes of these cells combine to form a delicate fibrillar background termed the neuropil . 

Myelin is a spiral structure made up of extensions of the plasma membrane from the myelinating glial cells, namely the oligodendrocytes in the CNS and the Schwann cells in the PNS. These cells send out sail-like extensions of their cytoplasmic membrane, each of which forms a segment of sheathing around an axon, which then constitutes the myelin sheath. 

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