The sting of a paper cut or the throb of a dog bite is perceived through the skin, where cells react to mechanical forces and send an electrical message to the brain. These signals were believed to originate in the naked endings of neurons that extend into the skin. But a few months ago, scientists came to the surprising realization that some of the cells essential for sensing this type of pain aren’t neurons at all. It’s a previously overlooked type of specialized glial cell that intertwines with nerve endings to form a mesh in the outer layers of the skin. The information the glial cells send to neurons is what initiates the “ouch”: When researchers stimulated only the glial cells, mice pulled back their paws or guarded them while licking or shaking — responses specific to pain.

This discovery is only one of many recent findings showing that glia, the motley collection of cells in the nervous system that aren’t neurons, are far more important than researchers expected. Glia were long presumed to be housekeepers that only nourished, protected and swept up after the neurons, whose more obvious role of channeling electric signals through the brain and body kept them in the spotlight for centuries. But over the last couple of decades, research into glia has increased dramatically.

“In the human brain, glial cells are as abundant as neurons are. Yet we know orders of magnitude less about what they do than we know about the neurons,” said Shai Shaham, a professor of cell biology at the Rockefeller University who focuses on glia. As more scientists turn their attention to glia, findings have been piling up to reveal a family of diverse cells that are unexpectedly crucial to vital processes.

It turns out that glia perform a staggering number of functions. They help process memories. Some serve as immune system agents and ward off infection, while some communicate with neurons. Others are essential to brain development. Far from being mere valets to neurons, glia often take leading roles in protecting the brain’s health and directing its development. “Pick any question in the nervous system, and glial cells will be involved,” Shaham said.

More Than Just ‘Glue’

Glia take many forms to perform their specialized functions: Some are sheathlike, while others are spindly, bushy or star-shaped. Many tangle around neurons and form a network so dense that individual cells are hard to distinguish. To some early observers, they didn’t even look like cells — they were considered a supportive matrix within the skull. This prompted the 19th-century researcher Rudolph Virchow to dub this non-neuronal material “neuroglia,” drawing on the Greek word for glue.