Defining Seizures

A seizure can be defined as abnormal, uncontrolled electrical activity in brain cells. Nerve cells transmit signals to and from the brain in two ways by (1) altering the concentrations of salts (sodium, potassium, calcium) within the cell and (2) releasing chemicals called neurotransmitters (gamma aminobutyric acid). The change in salt concentration conducts the impulse from one end of the nerve cell to the other.

At the end, a neurotransmitter is released, which carries the impulse to the next nerve cell. Neurotransmitters either slow down or stop cell-to-cell communication (called inhibitory neurotransmitters) or stimulate this process (called excitatory neurotransmitters).

Normally, nerve transmission in the brain occurs in an orderly way, allowing a smooth flow of electrical activity. Improper concentration of salts within the cell and overactivity of either type of neurotransmitter can disrupt orderly nerve cell transmission and trigger seizure activity.

Certain areas of the brain are more likely than others to be involved in seizure activity. The motor cortex, which is responsible for body movement, and the temporal lobes, including the hippocampus, which is involved in memory, are particularly sensitive to biochemical changes (e.g., decreased oxygen level, metabolic imbalances, infection) that provoke abnormal brain cell activity.

Seizure Phases

A seizure often has three distinct phases: aura, ictus, and postictal state. The first phase involves alterations in smell, taste, visual perception, hearing, and emotional state. This is known as an aura, which is actually a small partial seizure that is often followed by a larger event.

The seizure is known as ictus. There are two major types of seizure: partial and generalized. What happens to the person during the seizure depends on where in the brain the disruption of neural activity occurs.

Following a seizure, the person enters into the postictal state. Drowsiness and confusion are commonly experienced during this phase. The postictal state is the period in which the brain recovers from the insult it has experienced.

Publication Review By: Gordon R. Kelley, M.D., Stanley J. Swierzewski, III, M.D.

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Last Modified: 05 Aug 2011