Seizure foci

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  1. Epileptic seizure is a sudden alteration of CNS function resulting from a paroxysmal high frequency, high voltage electrical dischage arising from an assemblage of excitable neurons in any part of the cerebral cortex
  2. Cells of seizure foci have increased ionic permeability rendering them susceptible to activation by hyperthermia, hypoxia, and photic stimulation
    1. glutamate receptors on seizure cells may be involved in the pathogenesis of seizures
  3. Animal models show epileptogenic cells with profound calcium mediated paroxysmal depolarizing shifts (PDS) followed by prolonged after hyperpolarization (PAH)
  4. Neurons surrounding epileptogenic focus are hyperpolarized and GABAergic, inhibiting the neurons within the seizure foci; seizure spread depends on any factor or agent that activates neurons in the focus or disinhibits those surrounding it
  5. Seizure foci are more sensitive to ACh and are slower in binding and removing it than normal cerebral cortex; a deficiency of GABA, increased glycine, decreased taurine and decreased or increased glutamic acid have all been reported in excised human epileptogenic tissue
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