The chain of physical and chemical events in and around the brain that leads to migraine headaches is still unclear. What is known is that something activates a cascade of biochemical reactions that may trigger an inflammatory response and overexcitement of the trigeminal nerve, a major pain pathway which controls sensation in the face and head. This overexcitement spreads to other nerves in the meninges—the protective membrane covering the brain—and leads to pain and other migraine symptoms.