Epilepsy & EEG Flashcards
What are the two major excitatory neurotransmitters and what neurons typically form excitatory synapses?
Neurotransmitters:
- Glutamate (main)
- Aspartate
Principal neurons (Na+ and Ca2+ influx)
What are the two major inhibitory neurotransmitters and what neurons typically form inhibitory synapses?
Neurotransmitters:
- GABA (main)
- Glycine
Interneurons (Cl- influx, K- efflux)
Repetitive activation of action potentials produces what type of firing in neurons?
Burst firing
Burst firing especially occurs in what part of the brain?
Hippocampus
What does excessive glutamate result in?
Seizures
Activation of what type of receptors plays an important role in the spread of epileptic activity?
NMDA receptors
Describe “recurrent excitatory pathways” and their significance to seizures.
- Recurrent excitatory pathway occurs in the hippocampus and neocortex via pyramidal collaterals.
- This provides activation that is normally governed by widespread inhibitory circuits.
- Promotes spread of the seizure discharge.
What part of the brain anatomy promotes epileptogenesis?
Hippocampus
What hippocampal “disease” is common in temporal lobe epilepsy?
Hippocampal sclerosis (see in long-standing epilepsy)
How does hippocampal sclerosis affect epilepsy?
- Synaptic reorganization and increased axonal collateralization provide increased excitatory input between neurons. (the more seizures you have, the easier it is to have another one because connections are strengthened)
- This promotes synchronous epileptic firing and seizure propagation.
High frequency repetitive firing results in accumulation of what?
Ca2+ near the presynaptic terminal
How does high frequency repetitive firing (and accumulation of Ca2+ at the presynaptic terminal) result in synaptic enhancement?
- Facilitation: Increased glutamate release
- Potentiation: Enhanced synaptic activity
How does repetitive neuronal firing affect synaptic inhibition?
Repetitive neuronal firing DEPRESSES inhibitory (GABA) synaptic activity
Describe how electrical coupling of neurons affects epilepsy.
In areas with densely packed neurons (hippocampus), neurons may be connected directly via gap junctions, or ephaptic transmission due to close apposition of membranes, allowing direct propagation of seizure discharge.
What are the 5 major cellular mechanisms of epilepsy? (KNOW THIS)
- Modification or alteration of ion channels
- Synaptic reorganization and modificatoin
- Modulation of gene expression
- Burst firing
- Recurrent excitatory connections
- Synaptic enhancement and potentiation produced by rapid firing
- Depression of inhibitory synapses by high frequency firing
- Nonsynaptic spread of electrical activity
Define epilepsy.
Recurrent seizures produced by abnormal repetitive neuronal firing in the brain.
What is the most common cause of single seizures (especially in pediatrics)?
Febrile seizures
What are the two major categories of seizure?
Focal (partial)
Primary generalized