Seizures and epilepsy

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Seizures and epilepsy
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Seizure Temporary loss of control of a
Motor, Sensory or Psychological function (or a
combination of them) due to an unbalance between
excitation and inhibition
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Epilepsy A syndrome (group of diseases)
characterized by the recurrent occurrence of
seizures
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Ambiguous nature of the extracellular electric
signal
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The extracellular signal (EEG) represents the
ensemble activity of large groups of
neurons Small amplitude desynchronization of
single units Large amplitude synchronization
of many units
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Seizure synchronization of the activity in
different points of the brain
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Nature of the Paroxismal Depolarizing Shift PDS,
typical of seizures The mechanism is
reproducable in brain slices in the presence of
bicuculline Low Mg or NMDA agonist induce the
same This demonstrates that seizures are due to
local properties of the tissue
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Fragments of tissue cut and kept in physiological
conditions for up to 12 hours Voltage-gated
channels Axon and synaptic transmission Membrane
transporters Intracellular Ca stores Are
functional Advantage great electrical and
pharmacological access Drawback loss of
anatomical connections
Brain slices
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Roles of different membrane constituents within a
seizure
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Physiological and pathological role of inhibition
in spatio-temporal shaping of intracortical
activity epileptic focus
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Cortical neurons classification Excitatory cells
(pyramidal, spiny, A, B) Inhibitory cells
(non-pyramidal, smooth, C-I)
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Initiation and steady-state of a seizure
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Difference between Partial (focal) Secondaril
y generalized (spread) and Primary
generalized (absence) seizures
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EEG in a primary generalized seizure
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Similarity between primary generalized seizures
and thalamic-generated slow-wave spindles
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Focal epilepsy
Spread of activity from a focus
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Temporal lobe (hippocampal) atrophy
Removal of the epileptic focus substantially
decreased the symptoms
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Kindling induces gross morphological
cytoachitectonic and histological changes
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Possible propagation of hippocampal seizures as
electric signal propagation across several
hippocampal lamellæ