More than 700,000 strokes occur each year in the United States, making it the 3rd leading cause of death among Americans.  Strokes also cause many long-lasting disabilities for survivors.  If a stroke is this serious, what happens during a stroke and can strokes be prevented?  

What happens during a stroke?
Your brain needs a normal supply of blood to remain alive.  A person experiences a stroke when there is either too much or too little blood in the brain, which keeps brain tissue from receiving its normal supply, and therefore kills brain cells.  Because the brain can die within a matter of minutes, any suspicion of stroke should be treated as an emergency, and require immediate medical attention.

Two types of stroke

Hemorrhagic stroke - During a hemorrhagic stroke, a blood vessel breaks, and excessive blood flows into the brain.  One example of hemorrhagic stroke is called an 'intra-cerebral hemorrhage' wherein a blood vessel breaks, forcing blood to spill out and causing brain cell damage.  Thereafter, brain cells are no longer able to receive blood, and begin dying.  Another example of hemorrhagic stroke is called 'subarachnoid hemorrhage' in which bleeding originates from an artery on the surface of your brain (or, close to it) and blood remains between the brain and skull.  

Ischemic stroke - This type of stroke is the most commonly experienced form of stroke, and occurs when a blood clot prevents oxygen-rich blood from entering into the brain.  One example of an ischemic stroke is called an embolic stroke, where a blood clot forms in your heart or another place away from your brain, and then flows through the blood stream to eventually block a blood vessel in the brain.  The second type of ischemic stroke happens as a result of a clot that forms in your brain vessels, usually due to atherosclerosis.

Some people experience a transient, or "transitory ischemic attack" (TIA), wherein symptoms persist for a few minutes, but then disappear.  This is indeed a stroke, but a milder version and could also be called a "mini-stroke".  Nonetheless, an experience of transient ischemic stroke signals that an artery which is less than healthy, because it is blocked or smaller than what should be.  You should treat this as a medical emergency and get immediate medical care.