neuroinflammation

Neuroinflammation is the brain and spinal cord's version of the swelling, heat, and redness you feel when you cut your finger — an alarm-and-cleanup response, but happening inside nervous tissue where it cannot show up as a visible bruise. When something goes wrong (an infection, a head injury, a stroke, a toxin, or sick and dying cells), the nervous system's resident helper cells switch from quiet caretaking into an active defensive mode, calling for backup and trying to wall off and clear away the trouble.

The response is run mostly by glia — the support cells that vastly outnumber neurons. Microglia, the brain's built-in immune cells, are the first responders: they crawl toward the damage and release signaling molecules called cytokines, the chemical 'shout' that recruits more help. Astrocytes, star-shaped glia, react too, tightening around the injury. These signals can also loosen the blood–brain barrier (the brain's selective wall) so that immune cells from the bloodstream slip in. A short, well-aimed burst of this is healing — it removes debris and germs. But when the alarm stays switched on for months or years, the same molecules that were meant to protect begin to damage neurons, which is why long-running neuroinflammation is now tied to conditions like Alzheimer's disease, multiple sclerosis, chronic pain, and depression.