Virus infections, albeit with a very long period between initial infection and development of symptoms, are known to cause some other dementing illnesses. It is probably not quite right to call them viruses as the infective agents which are responsible for diseases like Creutzfeldt-Jakob disease are very unlike conventional viruses. There is also a rare brain disease which occurs in New Guinea and an infectious disease of sheep called scrapie in which an infectious particle of some sort appears to play a part as seerris to be the case too for the more recently publicized disease of cattle — bovine spongiform encephalopathy (BSE). The interrelationships, if any, between these conditions are complex but the fact that an infectious agent seems to be involved has led to the search for the presence of a virus or similar particle in Alzheimer’s disease. So far, none has been definitely implicated.
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April 2nd, 2009 :: Filed under
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The parietal lobe puts together all the information that our brains obtain in order to allow us to undertake quite complicated activities. For instance one of the characteristic problems experienced relatively early in the course of Alzheimer’s is difficulty with operating machinery or equipment such as a washing machine or television, and later with dressing. Difficulties like this, which are not caused by a specific abnormality in one of the nervous pathways outside the brain, are called apraxias. The presence of apraxias for a variety of activities usually indicates that the disease is going to progress fairly rapidly.
The parietal lobe also integrates the information that is obtained from the senses. Most people will be able to distinguish between a ten pence piece and a fifty pence piece when put in their hand, even if their eyes are closed so that they can’t see what the coin looks like. A person with parietal lobe damage won’t be able to do this and is said to be suffering from an agnosia.
A frequently employed test of parietal lobe function, which is really trying to elicit evidence of the presence of apraxia, is to ask the subject to draw or copy a diagram. This may be a simple clock-face or a more complicated structure such as intersecting geometric shapes.
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Our brain is such an important part of our body, even of our very existence, that it is protected by the bones of the cranial cavity within the skull. Any damage to the head sufficient to break the skull bones has serious consequences for the brain, ranging from loss of consciousness to permanent brain damage, with subsequent impairment of intellect or physical body function.
It is less well known that the brain also has other protective systems. These consist of a series of membranes and a fluid known as the cerebrospinal fluid (CSF). These are arranged in such a way that the brain is enclosed within a tough outer membrane called the dura mater, and within this lies another sack containing the CSF and the brain. Suspending the brain within the bag of fluid protects it not only from the day to day jolts that it would otherwise receive, but also from more serious damage — say a blow on the head that is insufficient to fracture the skull bones. Despite this protection, excessive physical force is still capable of causing damage, although this would be much greater if the fluid wasn’t present. The membranes also stretch tightly between the major subdivisions of the brain, thus limiting the degree to which any part of the brain can be displaced if physical trauma occurs. Our brain is therefore very well-protected from the outside world.
The brain is a pinkish structure, the pink colour coming from the blood that is circulating in the minute blood vessels that nourish the nerve cells. Each brain contains some 10 to 12 billion nerve cells – also called neurones. The brain is so important that it takes up about 20 per cent of the blood that our hearts pump out, and consumes a similar amount of the oxygen that we breathe in through our lungs. Despite requiring such a large amount of blood and oxygen it weighs only a fraction of our total body weight, usually in the region of 2-3 lb (1—1.5 kg). It is often assumed that the larger a person’s brain the more intelligent they are; this is fine for male chauvinists as in general men appear to have larger brains than women! Sadly, however, at least for us men, intelligence or other aspects of mental ability are not related to the size of the brain.
In order to allow us to understand more easily some of the illnesses that cause dementia, this chapter will describe some aspects of the structure of the brain, and how it works. The brain is, however, such an enormously complex organ that it would be confusing, and to a certain extent irrelevant, to explore these subjects at other than a simple level. The description that follows is, therefore, particularly arranged to take into account structures and functions that are important for the understanding of some of the dementing conditions.
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April 2nd, 2009 :: Filed under
General health