There are four types of glial cells in the CNS, they are listed below along with their functions:
a. Ependymal cells: These cells secrete cerebrospinal fluid. The cavities in the CNS filled with cerebrospinal fluid are lined by ependymal cells and help the movement of CSF in the tissues of CNS (brain and spinal cord).
b. Astrocytes: These are star shaped cells present throughout the brain. They form the supporting network in brain and spinal cord by twisting around the nerve cells. They contribute for the formation of blood brain barrier (BBB), thus restricts the entry of various substances from the vascular tissues into the brain. So, they regulate the chemical environment of the cerebrospinal fluid (CSF).
c. Microglia: These are the smallest neuroglial cells derived from monocytes, and enter into the tissues of nervous system through blood vessels. They function as phagocytes and migrate to the site of infection and so, they are also called as macrophages of central nervous system (CNS).
d. Oligodendrocytes: They produce myelin sheath around the nerve fibres of central nervous system, and provide support for these neurons.
e. Schwann cells: They myelinate axons of the peripheral nervous system (PNS). They provide nutrition to the neurons and helps in repair.
Thus, blanks can be filled with ependymal cells, astrocytes, microglia, oligodendroglia, Schwann cells; nourishing, waste removal, insulation of neurons, supporting, repairing.