Glial cells

Glial cells are the support cells of the nervous system. Each has a different structure and job.

Ependymal cells
Found on the walls of the ventricles. They secrete cerebrospinal fluid.

Astrocytes/Astroglia
Found in the CNS; they connect blood vessels and neurons, and hold them in place by attaching to the brain's lining. All substances exchanged by the blood and the neurons go through astrocytes. Only small substances can pass this blood-brain barrier, protecting the neurons from toxins.

Microglia
Originate in the blood, and are an offshoot of the immune system. They monitor the health of the brain tissue and acts as its immune system. They provide growth factors to damaged cells, and use phagocytosis against foreign tissue.

Oligodendroglia and Schann cells
These glial cells myelinate axons. Myeline speeds up the propagation of signals. Oligodendroglia myelinate the CNS, providing myelin for multiple cells at a time. Schwann cells myelinate the PNS, and each cell wraps itself around one axon.

Myelination begins just after birth, and continues until at least 20 years of age.