There are two kinds of stroke. In an ischemic stroke, a blood clot or narrowing of an artery prevents blood from getting to part of the brain, cutting off fragile brain tissues from their supply of oxygen and nourishment. In a hemorrhagic stroke, a blood vessel breaks, causing bleeding inside or around the brain. About half the people who later have ischemic strokes will first suffer transient ischemic attacks, or TIAs. In a TIA, a person suffers the symptoms of a stroke, but the symptoms go away in a few minutes.
Strokes can damage the brain in different ways.
In hemorrhagic stroke, the bleeding itself and the pressure buildup it causes can harm brain tissues. In both kinds of stroke, parts of the brain normally nourished by the affected blood vessel are cut off from their supply of blood and oxygen. These signals cause nerve cells to die in an area of the brain much larger than that affected by the blood blockage. When blood-supply cutoff and chemical deterioration threaten brain tissues, these tissues slowly start to die off. The stroke victim begins to lose the functions these tissues normally carry out.