When Stroke Strikes - How The Brain Works: Stroke

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When stroke strikes

The symptoms of a TIA or stroke provide clues about its type and its location in the brain. A stroke on the left side of the brain, for example, may result in confusion, abnormally slow movements, abnormal speech, an inability to speak or understand speech, or an inability to see objects in the right half of the visual field. People with this type of stroke may have difficulty reading, writing, or calculating. They may also become slow, cautious, and disorganized when faced with an unfamiliar situation.

People with right-sided strokes may ignore or fail to recognize objects or sensations on their left side or even neglect parts of the left side of their body. Deficits on the right side of the brain may also interfere with spatial perception, leading to difficulties with common tasks such as eating, drinking, dressing, operating a wheelchair, or reading. People with this type of stroke may engage in impulsive or dangerous behavior.

If you notice any telltale symptoms in yourself or in a loved one, dial 911 right away. A stroke is a medical emergency, and the sooner you seek treatment, the better.

The brain is especially vulnerable to injury, which is one reason it has a strong skull for protection. Although the brain accounts for only 2% of a person's total body weight, it uses about one-quarter of the body's oxygen and expends more than two-thirds of the body's chief source of energy, glucose. Despite these intense needs, the brain cannot store oxygen or glucose and therefore must be supplied by a constant flow of blood. Cutting off the brain's blood supply for only 30 seconds can cause unconsciousness, and after only 4 minutes permanent damage begins to set in. That's why it's important to get medical help quickly when the signs and symptoms of stroke first appear.

Blood delivers fuel and nourishment through a complex system of blood vessels that reaches every neighborhood of the brain (see Figure 1). The carotid arteries, which run up the left and right sides of the neck, are especially important, supplying blood to the front of the brain and the cerebral cortex (see Figure 4). The vertebral arteries, which run up the back of the neck and join at the base of the skull to form the basilar artery, supply the cerebellum, the brainstem, and the back parts of the brain. These major arteries join at the base of the brain to form the Circle of Willis, from which other vessels branch off. Problems in any of these blood vessels may lead to stroke.

Figure 4: Blood vessels matter It's important to understand which blood vessels are involved in a stroke, as this guides treatment. The carotid arteries, which run up the left and right sides of the neck, are particularly important, as they supply blood to the cerebral cortex, the part of the brain responsible for consciousness. One type of ischemic stroke can occur if atherosclerotic plaque builds up in the carotid arteries, while another type occurs after one of the carotid arteries tears. (The carotid arteries depicted above are healthy.) Courtesy of the 3D Imaging Laboratory, Massachusetts General Hospital

Last updated:	September 05, 2008