Glial cells are part of the nervous system, kind of woven throughout it, appearing more densely in some areas (the brain) than others (the fingertips.) They were formerly considered to be just support structures, but I remember, back around 1990, reading articles linking them to inflammatory processes in the brain. Therefore I figured they were part of the brain’s immune system, but science (and funding) didn’t make that short leap (inflammation to immune response) until recently. Now they’re considered key to the brain’s own immune system.
Astrocytes (‘astro’ means star; ‘cyte’ means cell) are a type of glial cell, named for their spiky, roundish, star-like shape. This article says that, in fruit flies at least, astrocytes regulate the sleep/wake cycle:
This is interesting because the circadian rhythm is disrupted in CRPS, and we’ve recently learned that astrocytes and other glial cells are disrupted by CRPS too. Assuming human’s astrocytes are functionally similar to fruit flies’ astrocytes, that circadian rhythm issue might be caused — or at least mediated — by those twinkling astrocytes.