What is a stroke?

Brain cell function requires a constant delivery of oxygen and glucose from the bloodstream. A stroke, or cerebrovascular accident (CVA), occurs when blood supply to part of the brain is disrupted, causing brain cells to die. Blood flow can be compromised by a variety of mechanisms.
Blockage of an artery

Narrowing of the small arteries within the brain can cause a lacunar stroke, (lacune means "empty space"). Blockage of a single arteriole can affect a tiny area of brain causing that tissue to die (infarct).

• Hardening of the arteries (atherosclerosis) leading to the brain. There are four major blood vessels that supply the brain with blood.The anterior circulation of the brain that 
• controls most motor  activity, sensation, thought, speech, and emotion is supplied by the 
• carotid arteries. The posterior circulation, which supplies the brainstem and the cerebellum, controlling the automatic parts of brain function and coordination, is supplied by the
•  vertebrobasilar arteries.

If these arteries become narrow as a result of atherosclerosis, plaque or cholesterol, debris can break off and float downstream, clogging the blood supply to a part of the brain. As opposed to lacunar strokes, larger parts of the brain can lose blood supply, and this may produce more symptoms than a lacunar stroke.

• Cerebral hemorrhage (bleeding within the brain substance). The most common reason to have bleeding within the brain is uncontrolled high blood pressure. Other situations includeaneurysms that leak or rupture or arteriovenous malformations (AVM) in which there is an abnormal collection of blood vessels that are fragile and can bleed.

• What causes a stroke?

  Blockage of an artery
  The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of blood and oxygen. As a result of the deprived blood and oxygen, the cells of that part of the brain die and the part of the body that it controls stops working. Typically, a cholesterol plaque in a small blood vessel within the brain that has gradually caused blood vessel narrowing ruptures and starts the process of forming a small blood clot.
  Risk factors for narrowed blood vessels in the brain are the same as those that cause narrowing blood vessels in the heart and heart attack(myocardial infarction). These risk factors include:
  high blood pressure (hypertension),