There are essentially two types of stroke: ischemic and hemorrhagic. In an ischemic stroke, the blood supply to a part of the brain is blocked wholly or partially, depriving brain cells of vital oxygen and nutrients. Within minutes, brain cells begin to die. Loss of function depends on where in the brain the blockage occurred.
In a hemorrhagic stroke, a blood vessel in the brain ruptures, causing sudden bleeding. The accumulating blood exerts pressure on brain cells, damaging them.
The vast majority of strokes—87 percent, according to the National Heart, Lung, and Blood Institute—are ischemic, the result of a blockage in a blood vessel.