General Nursing©

What You Should Know About Epilepsy?

The Physiology of a Seizure

In order to understand the process of electrical transmission within nerve cells, it is important to review the structure and function of a nerve. A nerve cell can be thought of as a tube, having an inner section, and bounded by a cell wall (membrane). Importantly, the chemical composition of the inside of the cell and the outside of the cell are very different. Specifically, there is a difference in the concentration of sodium and potassium salts, with sodium being much higher on the outside, and potassium being much higher on the inside. In a normal resting state, special pumps (called membrane pumps) are continually at work to maintain each salt in its proper location.

When a nerve is called upon to transmit an electrical signal, a sudden movement of these salts from one side of the cell's membrane to the other occurs. This movement spreads like a wave from one end of the nerve to the other, until it reaches the end. At this point, the nerve's signal may be transmitted to the next nerve cell either by a direct extension of this process, or, more commonly, by releasing a special chemical called a neurotransmitter. Neurotransmitters generally have one of two special functions. One type is responsible for encouraging cell-to-cell communication and is referred to as an "excitatory" neurotransmitter. The second type is able to slow down, or even stop cell-to-cell communication and is called an "inhibitory" neurotransmitter. In some cases, over activity of excitatory neurotransmitters or under activity of inhibitory neurotransmitters may lead to seizure activity by allowing an uncoordinated flow of electrical activity in the brain.
Interestingly, certain areas of the brain are more likely than others to be the source of a seizure. These include the motor cortex (responsible for the initiation of body movement) and the temporal lobes (including a special deep area called the hippocampus, which is involved in memory). The reason for this likelihood may be that nerve cells in these areas are particularly sensitive to certain situations that can provoke abnormal electrical transmission. Examples include sensitivity to decreased oxygen levels, metabolic changes, and infection, any of which may lead to a seizure.

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