There are a few different types of glia in the brain: oligodendrocytes, microglia, and astrocytes. Each is needed to optimize brain function.
Oligodendrocytes are specialized cells that wrap tightly around axons to form the myelin sheath. These cells speed up the electrical signals (action potentials) that travel down an axon. Without oligodendrocytes, an action potential would travel down an axon 30 times slower!
Microglia are special immune cells found only in the brain that can detect damaged or unhealthy neurons. They eat foreign invaders (bacteria and viruses), then display the chewed up parts on their cell surface to signal for help.