Microglia or “microglue cells” constitute 5-20 percent of the entire glial population in the brain (e.g., nearly one microglial cell for every neuron). They are the smallest and most dynamic of all glia, able to transform into a highly mobile amoeboid cell whenever infection or injury is detected. Microglia orginate from the same embryonic line that gives rise to other immune system cells in the body. They enter the part of the embryo that will become the brain at a very early stage in development and grow up with the brain. They have a powerful ability to resupply their ranks by rapid cell division (something neurons cannot do). (Fields, R. Douglas, PhD. The Other Brain. p 41-44. NY: Simon & Schuster, 2009.)

Microglia can track down and devour bacteria, viruses, and cellular debris. They may also attack invaders with chemical agents (e.g., glutamate, cytokines, reactive oxygen, nitrogen species) that can be harmful to neurons in high concentrations.(Fields, R. Douglas, PhD. The Other Brain. p 44. NY: Simon & Schuster, 2009.)