Pathways of the CNS also contain myelinated axons, andwhen a disease such as multiple sclerosis leads to demyelination, there arechanges in affect, reasoning, and thought, as well as expected changes inskeletal muscle movement and strength. Neuroglia are the supportive cells of nervetissue. These cell types do not normally conduct electrical signals, but ratherperform other functions vital to the nervous system. Neuroglia includesastrocytes, ependymal cells, microglia, oligodendrogliocytes, Schwann cells,and Satellite cells. Astrocytes surround blood vessels that course througha thebrain, controlling what may cross the blood vessels to enter brain.
Microglia have phagocytic functions,scouring up dead cells and cleaning up debris.
Schwann cells and oligodenrogliacreate myelin sheaths as already described. The CNS, when cut, can be visualized with thenaked eye as consisting of white and grey substance, or matter. Grey matterconsists primarily of cell bodies, whereas white matter consits primarily ofcell axons. Meninges Both the CNS and PNS are enclosed byconnective tissue coverings. The meninges occur in three layers.