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WHY DO SEIZURES OCCUR? PHYSIOLOGY OF THE BRAIN

Posted on January 17th, 2011, by admin

Only by understanding something about the physiology of the brain— how it works—and its anatomy can we understand the many different types of seizures that can occur and consider why they happen.
The brain works on electricity, with neurons (nerve cells) communicating and interacting by discharging or “firing” tiny electrical impulses along interconnecting “wires” called axons. The electrical impulse results in the release of a chemical called a neurotransmitter from the axon’s ending or terminal that then interacts with the next cell. These chemicals (neurotransmitters) can be excitatory, that is make the next cell more likely to fire or inhibitory, that is cause the next cell to be less likely to fire. Each cell has many thousands of endings; some of them (excitatory) are telling the cell to say “yes” and increasing the chance of that cell’s “firing.” There are some endings on the cell that say “no” (inhibitory), decreasing the chance of that cell’s “firing”. The balance of these excitatory and inhibitory impulses influences its threshold, or how readily that cell can be stimulated to fire. The increase or loss of influences saying “no” can also decrease or increase that cell’s likelihood of “firing.”
One cell firing alone does not cause a seizure or even a movement, as we have said. For a muscle movement, such as a twitch of a finger, to occur, many hundreds of cells must fire together. The process involves “recruitment” of a sufficient number of neighboring cells to fire simultaneously. If not enough cells are “recruited” then not enough muscle fibers contract (shorten) to move the muscle. When you purposely move your finger, some muscle fibers on one side of the finger joint slowly contract (pull) in a coordinated fashion. The movement is controlled by the relaxation of muscle fibers on the other side of the joint (fired by different brain cells). This coordination and interaction of different groups of brain cells that control the muscle fibers on each side of the finger joint allow you to manipulate finger movement. If, however, one group of cells in the brain fires without the controlling influence of other cells your finger jerks or twitches. This is what happens in some types of seizures.
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