Brain cells. Scanning electron micrograph (SEM) of cortical neurons (nerve cells) on glial cells (flat, dark grey), showing interconnecting dendrites. Cortical neurons make up the brain cortex (grey matter). Glial cells are nervous system cells that provide structural support and protection for neurons (nerve cells). In the human brain, the most concentrated region of glial activity is in the cerebral cortex, where there are about four glia for every neuron. Magnification: x1447, when printed 10 centimetres wide.