The brain is arguably the most complex of all the organs in your body. These three pounds of tissue compose the major nerve center of the body, which coordinates all of our bodily functions, including behavior, thought and emotions. Because your brain is a very hard-working organ, it requires constant supplies of oxygen and nutrients from the blood to function effectively. The heart pumps blood throughout the cerebral arteries ("cerebral" means "related to the brain"), delivering blood to the brain. Any significant interruption to this supply of nutrients and oxygen will start killing brain cells. Damage to brain cells occurs almost immediately upon cessation or even significant restriction of blood flow to the brain. Minor damage to any part of the brain can have a serious adverse effect on the rest of the body. Significant damage to the brain can even result in death.
One relatively common cause of brain damage and death is referred to as a stroke. A stroke is similar to a heart attack, only in this case, blood flow to brain, rather than the heart, is blocked. The term "stroke" comes from the once popular idea that someone had received a "stroke of God's hand" and was therefore damaged. Strokes are also called cerebrovascular accidents (CVA's; "cerebrum" is Latin for brain, while "vascular" refers to the blood vessels) or "brain attacks" to emphasize the need to call 911 and get immediate medical attention when they occur.
Arterial blood vessels feeding the brain can become blocked on a permanent or temporary basis. The term stroke is generally reserved for more permanent blockages that do not rapidly and spontaneously resolve themselves. These blockages result in permanent brain damage and leave lasting physical or mental deficits. Transient and temporary blockages are called Transient Ischemic Attacks (or TIAs for short). TIAs temporarily alter behavior and thinking (for less than 24 hours), but do not end up creating lasting brain damage. Because the damage is temporary, a TIA is sometimes referred to as a "mini" or "warning" stroke. Individuals who experience TIA's are at greater risk for having serious strokes in the future.
There are two major ways that strokes generally occur:
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Ischemic strokes occur when a blood clot (called a "thrombi") or a fatty plaque (composed of fat deposits, cholesterol, and waste products) blocks blood flow to an area of the brain, causing death of the associated neurons (brain cells). Fatty plaques often line the interior artery walls of people with a cardiovascular disease called arteriosclerosis ("hardening of the arteries"). These plaques narrow the arterial space, and serve as points around which blood begins to clot. Resulting thrombi start to block the artery, which reduces the amount of blood able to pass through, and therefore the amount of oxygen getting to the cells is reduced. The clots can also detach and float downstream (they are then referred to as emboli), block blood flow to brain areas, and cause subsequent brain damage. Approximately 88% of strokes are ischemic events.
Hemorrhagic stroke, occurs when a cerebral (brain) artery ruptures and spills blood over the brain tissue. This spilled blood ends up pooling inside the skull, exerting pressure on and causing damage to delicate brain tissue. In addition, the ruptured vessels fail to do their typical job of feeding blood to specific areas of the brain. Between being starved for oxygen and nutrients, and being squeezed by the pressure of spilled blood, the brain ends up being severely injured or destroyed. Approximately 12% of strokes are hemorrhagic.
Approximately 700,000 Americans suffer a stroke each year. It is the third major cause of death in the United States each year after heart disease and cancer. In 2002, 162,672 individuals died of stroke in the United States.
Though strokes can be lethal, there are many people who survive them. However, these stroke survivors typically experience a range of limitations. For example, people might lose the ability to comprehend language, to speak, to walk, or to control parts of their body. As a general rule, the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body. So, individuals who had a stroke affecting the right side of their brain will probably have some difficulty controlling some portion of the left side of their bodies, and vice versa.
Due to concept called "neuroplasticity", healthy areas of the brain are sometimes able to compensate for abilities lost to stroke. Therefore, many people experience partial recovery of pre-stroke abilities.