Archive for the ‘Epilepsy’ Category

posted by admin on Feb 20

The threshold is the level of excitement at which a neuron will fire. As we have indicated, a cell’s threshold is determined by the excitatory and inhibitory influences upon it. The seizure threshold is the level at which
the brain will have a seizure, at which multiple cells will fire simultaneously.
Chemical factors, lack of oxygen, low calcium can lower the threshold as can fever, excitement, lack of sleep. In general, the brain has a large margin of safety to protect it from misfiring. The size of this margin of safety is determined genetically. As a consequence, some people are closer to the threshold than others. In individuals with a previously low genetic threshold, fever may cause an event known as a “febrile,” or fever-induced, seizure. Seizures can be produced in anyone if the temperature becomes sufficiently high (107° to io8°F) and if the brain becomes sufficiently excited. In those with a lower genetic resistance or threshold, a febrile seizure may occur at a temperature of 1o3°or 104°. If the threshold of an individual is quite low, a seizure may occur with only slightly increased excitement, at 1010 or 102°. Similarly, mild head trauma may cause a seizure in a child with a low genetic threshold, whereas it would take far more severe head trauma to cause a seizure in a child with a higher threshold.
The threshold for a seizure is dependent also on age. Young children have lower seizure thresholds than adults. That is why young children are more likely to have a seizure when they get a fever and why most epilepsy begins in childhood. The increase in threshold with age may be the reason why most epilepsy that has begun in childhood is outgrown.
Emotional factors and other physical factors also influence a child’s margin of safety. Excitement in response to a birthday party or a trip, or agitation caused by an argument or punishment, or anxiety during an exam may lower the individual’s margin of safety and cause a seizure. So may lack of sleep in an individual whose threshold is already low. Such interactions of genetic threshold and environmental influences may explain many single, presumably “spontaneous,” seizures.
Chemical changes in the blood, such as low blood sugar or low calcium levels, make neurons more susceptible to firing but are usually insufficient of themselves to produce seizures except in a “low-threshold, seizure-prone” child.
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posted by admin on Apr 28

A tumour arising within the brain understandably causes great anxiety-perhaps more so than with tumours elsewhere in the body, as a brain tumour may appear to strike at the very centre of one’s soul and being. Many people with simple headaches due to anxiety or stress believe that they have a brain tumour which is causing their headache. However, the incidence of primary tumour is very low (10 per 100 000 per year). It is, however, true that tumours can cause epilepsy. This is much more likely to happen in adults than in children.

Brain tumours are either primary or secondary. A secondary tumour is one that has been carried in the blood to the brain from another site. Cancers of the lung (bronchus) or breast are by far the most common of these. Usually the site of the original cancer is known, and the appearance of seizures in such a patient is an ominous sign indicating that a secondary tumour has arisen within the brain. Sometimes, however, the original cancer has not been discovered at the time of the first seizure, and a careful clinical examination will reveal a small tell-tale lump in the breast, or the lung cancer will be seen on a chest X-ray.

Primary tumours of the brain do not arise in nerve cells. These tumours are called gliomas and meningiomas. There are other types of primary cerebral tumours, such as those arising from the cells lining the cavities of the brain, or from blood vessels, but these are rare.

Primary brain tumours are not like cancer of the breast, or bowel, or bronchus. They show no tendency to develop blood-borne secondary deposits in other organs. This is fortunate, but there are other characteristics which hinder effective treatment. The gliomas infiltrate normal brain extensively, so there is no apparent margin beyond which one can be quite certain that no abnormal cells have reached. This makes recurrence after surgical excision very likely. Meningiomas, however, are encapsulated tumours, and can often be removed completely, with a good chance of complete eradication. However, meningiomas often have an extensive blood supply, so complete removal may be technically very difficult.

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