What is a Stroke?

Ask someone this question and you're liable to get an answer something like, "Well, you know, it's that thing that leaves people partially paralyzed." But many people don't actually know what causes a stroke or even where in the body it occurs. A stroke can be any one of three significantly different problems with blood supply to the brain, according to the American Medical Association.

Thrombosis (40-50 percent of cases): A clot builds up on a brain artery wall, cutting off blood supply and causing tissue in parts of the brain to die.

Embolism (30-35 percent of cases): A clot is swept into a brain artery and then clogs the artery.

Hemorrhage (20-25 percent of cases): A blood vessel in the brain ruptures.

Given these varying causes, and the fact that a stroke can occur in any part of the brain, symptoms can develop suddenly or over days, and outcomes vary dramatically, from headache and dizziness to paralysis or death. Stroke is the third leading cause of death in the United States.

Advice from the U.S. Centers for Disease Control and Prevention: "Knowing the symptoms of stroke, calling 911 right away, and getting to a hospital are crucial to the most beneficial outcomes after having a stroke. The best treatment is to try to prevent a stroke by taking steps to lower your risk for stroke."

• CDC Stroke Information