A stroke occurs when a blood clot blocks an artery or a blood vessel ruptures and interrupts blood flow to an area of the brain. The most common places where clots form are in the carotid arteries and in the heart when there is atrial fibrillation. When blood flow is interrupted to the brain by these mechanisms, brain cells die or become malnourished so that they are stunned and unable to function.
When brain cells die during a stroke, abilities controlled by that area of the brain are lost. These abilities include speech, movement and memory. How a stroke patient is affected depends on where the stroke occurs in the brain and how much the brain is damaged.
Transient ischemic attacks (TIAs) occur when blood flow is obstructed for only a short time (less than a day) and before there is actual tissue death. They are often a warning sign that a stroke is impending.