When a person with a lowered threshold to headache comes in contact with a trigger, a series of events begins. Sometimes migraine triggers are obvious, like drinking red wine, having your menstrual period, or having a stressful day; other times, triggers are less clear and may be internal changes in the body of which we're unaware.
After the migraine process has been initiated, nerve cell activity in the back of the brain (the occipital, or visual, cortex) begins moving to the front to the brain. This wave of nerve activity is noted on both sides of the brain. The wave initially causes the nerve cells to be less active, and a wave of increased nerve activity follows. Because migraine activity often begins in the part of the brain affecting vision, many migraine sufferers experience visual changes during their attacks, such as migraine auras and blurred vision. An area of the brain called the hypothalamus is also activated. This causes the vague feelings of irritability, anxiety, hyperactivity, food cravings, and increased urination that are reported as prodrome symptoms by some people with migraine.
As the nerves become activated, the ends of the nerves next to blood vessels in the scalp (outside the skull) release certain chemicals, such as serotonin, which cause the blood vessels to expand or dilate and become inflamed. These expanded blood vessels cause an increase in the blood flow around the brain. As a result, you may notice that the blood vessels at your temples increase in size and are tender. Other chemicals are also released from the nerve endings, leading to more dilated and inflamed blood vessels. These dilated, inflamed blood vessels further stimulate the nerve endings to release more chemicals, thereby amplifying the process.
Once nerve activation starts, nerves located in the brainstem begin to send migraine messages throughout the brain. Pain signals are transmitted to the muscles in the neck, which become stiff and painful. This causes the neck pain that is often seen during both the prodrome and headache phases of migraine. Pain signals also travel to the part of the brain sometimes referred to as the "nausea center," resulting in loss of appetite, nausea, and sometimes even vomiting. Pain messages also travel to pain centers in the brain, further amplifying the pain response. Resulting in what some people call a "full-blown" migraine.