Partial seizures

Neuronal network dysregulation Partial seizures

With partial seizures, the focus is most often localized in the frontal or temporal region and the seizure remains within the hemisphere.

The seizure starts with increased electrical activity in a single excitatory neuron. This sudden depolarisation is called a paroxysmal depolarizing shift and can be caused by changes in the cellular environment. The inhibitory control within the neuronal network is no longer able to control the repetitive action potentials.

The mechanisms underlying the override of the inhibition could include increased extracellular potassium ions and opening of the voltage-sensitive NMDA-channels. The most important mechanism however, is the decrease in GABA-mediated inhibition (as shown). All these events lead to propagation of the signal and local synchronization. If the synchronization is strong enough, the firing of the small neuronal network will spread to adjacent cortical regions.

1

Normal neuronal activity depends on adequate concentrations of all the following EXCEPT: