A mere 15% of the cells in our brains are neurons. The other 85% of our brain cells are called glia—short for neuroglia—Latin for “neural glue.”

Glia outnumber neurons six to one.

Up until fairly recently these glial cells were seen as very minor players—as evidenced by the name—simply forming the matrix of the brain, giving it structure, supporting the neurons and perhaps, performing a bit of housekeeping in the brain.

But subsequent to a new look at glial cells, following an odd and fascinating story about Einstein’s brain, the function of glial cells continues to emerge as critical to both neuronal and overall brain function.

In hindsight, given the capacity and marvel of the human brain, it seems foolish to have believed that 85% of our brains had primarily a structural role.

Unlike the physical connection of neurons (e.g.: synapse—dendrite—cell body—axon—synapse), glia are not structurally connected to each other and do not generate electrical impulses. Generally speaking, this means that glia communicate broadly, not linearly like neurons (think of the bouncing signals of cell phones vs. the direct connections of telephone lines) and glia communicate slowly.

There are four types of glial cell—Oligodendrocytes, Schwann Cells, Microglia and Astrocytes—performing distinct functions..

R. Douglas Fields, PhD in his extraordinary book, The Other Brain, summarizes glia function:

“Here are cells that can build the brain of a fetus, direct the communication of its growing axons to wire up the nervous system, repair it after it is injured, sense impulses crackling through axons and hear synapses speaking, control the signals neurons use to communicate with one another at synapses, provide the energy source and substrate for neurotransmitters to neurons, couple large areas of synapses and neurons into functional groups, integrate and propagate the information they receive from neurons through their own private network, release neurotoxic or neuroprotective factors, plug and unplug synapses, move themselves in and out of the synaptic cleft, give birth to new neurons, communicate with the vascular and immune systems, insulate the neuronal lines of communication, and control the speed of impulse traffic through them. And, some people ask, ‘Could these cells have anything to do with higher brain function.’ How could they not? ”

As if that isn’t enough, these new superstars of the brain—glial cells, have now been linked to performing a vital function in sleep, perhaps even providing an explanation as to why we sleep.

Recent studies suggest that glial cells swell (when awake) and shrink (in sleep) to control the glymphatic system—the brain’s drainage system, and the flow of cerebral spinal fluid throughout the brain.

The increased flow in sleep is described as “opening spigots that bathe the brain in fluids and wash away potentially toxic build-ups. Ultimately, the fluid and any debris it carries washes into the liver for disposal.”

It is the literal form of brain washing, like hosing down the brain getting rid of the garbage and getting it ready for a new day.