Type of glial cell	Origin	Appearance	Functions
Astrocytes	Neuroectoderm	Round vesicular nuclei Contain glial fibrils, composed of glial fibrillary acidic protein	• Repair • Structural & metabolic support • Blood-brain barrier • Remove excess neurotransmitters, related with Hyperammonemia
Oligodendrocytes	Neuroectoderm	Small nuclei surrounded by a pale halo Fewer processes than astrocytes	• Myelinate axons in the CNS, including CN II • Main glial cells in the cerebral white matter
Microglia	Primitive yolk sac macrophages	Small elongated nuclei Many short branching processes	Special macrophages in CNS, i.e. phagocytic
Ependymal cells	Neuroepithelial cells (neuroectoderm)	Simple columnar glial cells	Form the epithelium lining the ventricles and central canal of the spinal cord

Mnemonic

Glial cells guard the axons of the nerve cells as COPS: CNS axons are myelinated by Oligodendrocytes; PNS axons are insulated by Schwann cells. Oligodendrocytes → multiple sclerosis Schwann cells → Guillain-Barré syndrome