Neurophysiology and epileptogenesis Flashcards
Epileptogenesis
The process by which parts of a normal brain are converted to a hyperexcitable brain
Epileptic seizures
An explosion of synchronous activity by lots of neurones at once that has a tendency to spread through the cerebral cortex
A brief change in behaviour caused by the synchronous and rhythmic firing of action potentials by populations of neurones in the CNS
Why os the brain prone to seizure activity?
Due to action potentials
Chain reaction can lead to progressive spread over large area
Epilepsy represents failure of inhibitory regulation
Na+ channel inactivation too slow
e.g. generalised epilepsy with febril seizures
Point mutation in part of na+ channel
Action potential repolarisation impaired
Reduction in the number of functional K+ channels
e.g. benign familial neonatal convulsions
Defect in KCNQ2 or KCNQ3 K+ channel subunit
Action potential repolarisation impaired
Ion channels and epilepsy
Na+ channel inactivation too slow
Reduction in the number of functional K+ channels
The electroencephalogram
Recording with array of electrodes on scalp gives information about electrical activity of very large numbers of neurones in cerebral cortex
Largest potentials recorded when brain is at rest
EEG without sensory inputs
Various neural networks feedback upon themselves
Leads to rhythmic oscillations
EEG when arrous
Neuronal activity becomes desynchronised
Hyperexcitation of seizure leads to synchronous activity on EEG
Focal seizures origin
Originate within small group of about 1000 neurones
Synchronised paraozysmal depolarising shift overcomes inhibition
Increased extracellular K+
Train of action potentials occur
Secondary generalisation origin
Focal seizures spread to other brain regions along normal neuronal pathways
Show secondary generalisation if activity spreads to thalamus
(tonic clonic seizures)
