80% of all strokes are Ischemic Strokes
Ischemic strokes occur if blood flow is blocked locally in an artery supplying the brain or if the entire circulation fails so that all organs, including the brain, are inadequately perfused (this is what happens in shock).

What might block a brain artery?
1. Pathology such as atherosclerotic plaque in the vessel's wall that narrows or even obliterates its lumen (the inner channel through which blood flows), or produces complete collapse of the wall

2. A "plug" in its lumen formed by material carried in the blood

3. Abnormally high pressure in brain tissue surrounding the vessel that compresses its wall to the point of squeezing shut its lumen.