Pathways of the CNS also contain myelinated axons, and when a disease such as multiple sclerosis leads to demyelination, there are changes in affect, reasoning, and thought, as well as expected changes in skeletal muscle movement and strength. Neuroglia are the supportive cells of nerve tissue. These cell types do not normally conduct electrical signals, but rather perform other functions vital to the nervous system. Neuroglia includes astrocytes, ependymal cells, microglia, oligodendrogliocytes, Schwann cells, and Satellite cells. Astrocytes surround blood vessels that course througha the brain, 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 oligodenroglia create myelin sheaths as already described. The CNS, when cut, can be visualized with the naked eye as consisting of white and grey substance, or matter. Grey matter consists primarily of cell bodies, whereas white matter consits primarily of cell axons. Meninges Both the CNS and PNS are enclosed by connective tissue coverings. The meninges occur in three layers.