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
Oligodendrocytes	Neuroectoderm	Small nuclei surrounded by a pale halo Fewer processes than astrocytes	Production of myelin
Microglia	Primitive yolk sac macrophages	Small elongated nuclei Many short branching processes	Phagocytosis

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