What Is A Stroke: Stroke

Content provided by the Faculty of the Harvard Medical School

What is a stroke?

The brain relies on a steady supply of oxygenated blood to perform its myriad tasks — everything from coordinating your arm and leg movements as you walk down a street to allowing you to appreciate the complexity of language in a favorite novel. Because maintaining a steady blood supply is so important, multiple blood vessels snake into and around the brain, ensuring that even if one blood vessel becomes narrowed or damaged, alternate delivery routes still exist (see Figure 1).

Figure 1: Your brain's blood supply There is more than one arterial pathway that supplies your brain with the all-important blood it needs. Your brain has four main arteries delivering blood: two internal carotid arteries (A) and two vertebral arteries (B). If one of these becomes narrowed or blocked, your brain may be able to get the blood it needs via one of the other arteries connected by the Circle of Willis (C), which links the four arterial pathways (see inset).

A stroke occurs when an injury to a blood vessel supplying the brain causes it to burst, resulting in a hemorrhagic stroke, or becomes blocked, resulting in an ischemic stroke. In both cases, the injury deprives the brain of a constant blood supply carrying oxygen and nutrients; some of the cells of the brain die, possibly taking with them the ability to move, speak, feel, think, or even recognize people. In this way, a stroke threatens the very core of one's humanity.

Recovery after a stroke depends on how well healthy areas of the brain take over duties that had been performed by the damaged brain tissue. To some extent, especially in children and young adults, recovery is possible because of the brain's ability to compensate for damage in one area by working harder in another — by relying on alternate wiring for some functions or by rewiring around the injured site. In some cases, rehabilitation techniques can also facilitate functional recovery.

Last updated:	September 05, 2008