As their name implies (Latin and\or Greek for glue), glia help keep things together. Questions about the ratio of glial cells to neurons abound. Some have said a 9:1 ratio; others that 80% are glias. Recently, neurophysiologist Suzana Herculano-Houzel and colleagues have developed a new technique for estimating numbers of glial cells. An interesting finding is that rather than an overall constant glia-neuron ratio, the numbers change in different parts of the brain (e.g., there are much higher numbers of glial cells in the cerebral cortex as compared to the cerebellum). Regardless of the true glia to neuron ratio, scientists have already shown that glia are, functionally, the brain’s other half: some watch for bacteria and viruses that infect the brain and then mobilize to fight the invaders, others form myelin insulation to coat neuronal axons, while still others secrete food for neurons. (Source)

Glial cells outnumber neurons by at least 6 to 1 but the ratio differs in different parts of the nervous system. The ratio can be 100 glials to 1 neuron along nerves in the white matter tracts in the brain; in the frontal cortex the ratio is 4 to 1. Interestingly, whales and dolphins have 7 glials for every neuron in their gigantic forebrains. (Fields, R. Douglas, PhD. The Other Brain. p 24. NY: Simon & Schuster, 2009.)