Step inside the human body to see how your brain and vascular system are vitally linked to keep you alive and well. Though your brain occupies only 5% of your body, it needs 20% of the blood supply to function properly. When that blood supply is restricted or blocked, the life-giving oxygen in the blood can't get to the delicate brain tissues that need it. The tissues start to die, and parts of the brain stop working. You can think of a stroke as the same as a heart attack, except it happens in your brain.

In this video, you can see a stroke "in action," understand the different types of strokes, the causes, the symptoms to look for, what to do in an emergency and what you can do to avoid one.

VO: Your brain occupies only 5 per cent of your body...but needs 20 per cent of your blood supply to keep you functioning properly. Without that blood supply, things go wrong.

John Lucas: I knew I was in trouble, because I knew that the words were coming out garbled. I knew what I wanted to say. I was completely cognizant of everything going on around me. I guess that probably was just the scary part of it.

Dr. Castaldo: Stroke-like symptoms often last about ten or fifteen minutes and they involve face, arm, and leg, or at least face and arm, some slurred speech, some loss of vision or some difficulty getting words out. Those are telltale signs that the brain is under attack .

Dr. Castaldo: And this is a time to take action. Uh, if you come to the emergency room quickly there are often drugs that doctors can give you, which will break up that clot, clot busters if you will and stop the attack. And if we can stop that initial attack and then discover what`s going wrong, we can avert a stroke.

VO: A stroke can be thought of as a "brain attack," because just as heart tissue is starved by a heart attack, the brain tissue starts to die in a stroke. And the results can lead to paralysis, loss of other bodily functions or memory loss.

Dr. Fail: A person has a stroke and...it can be absolutely devastating. Uh, the first leading cause of disability, the third leading cause of death.

VO: There are two types of strokes: Ischemic and Hemorrhagic. Hemorrhagic Strokes occur when a blood vessel in your brain leaks or ruptures. The most common causes for this are uncontrolled high blood pressure, also known as Hypertension, or a weak spot in the walls of the blood vessel, called an aneurysm.

VO: If a cerebral aneurysm is detected, it can be treated with a surgical clip to avoid a potential stroke.

VO: But more than 80% of strokes are ischemic, which means they`re caused by a blockage of blood flow to the brain...sometimes when blood can`t get to the brain, and sometimes when a clot travels from elsewhere in the body, usually the heart, and becomes lodged in the brain.

Dr. Castaldo: The brain is a wonderfully vascularized organ, which means it has lots of blood supply. It has two major arteries in the front here called the carotid arteries, often as big as your index fingers. And two smaller ones in the back, a little smaller than your pinky, that come up to feed it.

VO: Doctors measure blood flow and determine if you are at a major risk for stroke with a variety of screening tools like ultrasound, echocardiogram, angiogram, CT scan, MRI, blood tests and physical exams.

VO: They can help prevent ischemic strokes with procedures like Carotid endarectemy, which surgically removes plaque from the vessels in the neck, and angioplasty, which widens blocked vessels, and also with medication.

VO: Some people suffer stroke-like symptoms in the form of a "mini-stroke," or what doctors call a TIA.

Dr. Castaldo: The term uh, TIA or transient ischemic attack uh, traditionally what it means is it`s a warning attack of a stroke. It means that for a short period of time a blood vessel has been blocked by a clot or a thrombus as we call it, that that tissue has suffered lack of oxygen for a period of time and then that clot has dissolved and blood has been restored and patients get better.

VO: A TIA is a wake up call to take action.

Dr. Goodreau: If you`ve had a stroke warning and don`t uh, pay attention there`s probably a pretty good, 20-30-40%, chance of you having a stroke within the next year or so.

VO: Other factors that put you at higher risk are: a family history of strokes, high-blood pressure, high cholesterol, obesity, diabetes, smoking, taking birth control pills, using illicit drugs - like cocaine - and high stress.

VO: Controlling these risk factors with healthy lifestyle choices and medication are your best bet for avoiding a stroke.