Cerebral “Stroke” Occurs When Cerebral Blood Vessels Are Blocked
Almost all elderly people have blockage of some small arteries in the brain, and as many as 10 per cent eventually have enough blockage to cause serious distur-bance of brain function, a condition called a “stroke.” Most strokes are caused by arteriosclerotic plaques that occur in one or more of the feeder arteries to the brain. The plaques can activate the clotting mechanism of the blood, causing a blood clot to occur and block blood flow in the artery, thereby leading to acute loss of brain function in a localized area.
In about one quarter of people who develop strokes, high blood pressure makes one of the blood vessels burst; hemorrhage then occurs, compressing the local brain tissue and further compromising its functions. The neurological effects of a stroke are determined by the brain area affected. One of the most common types of stroke is blockage of the middle cerebral artery that sup-plies the midportion of one brain hemisphere. For instance, if the middle cerebral artery is blocked on the left side of the brain, the person is likely to become almost totally demented because of lost function in Wernicke’s speech comprehension area in the left cere-bral hemisphere, and he or she also becomes unable to speak words because of loss of Broca’s motor area for word formation. In addition, loss of function of neural motor control areas of the left hemisphere can create spastic paralysis of most muscles on the opposite side of the body.
In a similar manner, blockage of a posterior cerebralartery will cause infarction of the occipital pole of thehemisphere on the same side as the blockage, which causes loss of vision in both eyes in the half of the retina on the same side as the stroke lesion. Especially devas-tating are strokes that involve the blood supply to the midbrain because this can block nerve conduction in major pathways between the brain and spinal cord, causing both sensory and motor abnormalities.
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