Glia cells.

1. Ependymal cells are ciliated to circulate cerebrospinal fluid.

2. Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) form myelin sheaths around axons.

3. Microglia protect the nervous system from microorganisms.

4. Astrocytes perform many functions, helping to form a blood-brain barrier in the CNS.