Epilepsy and MS

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  • Created by: Jess
  • Created on: 14-05-14 21:32
What is epilepsy?
A chronic disease that leads to repetitive seizures due to temporary abnormal CNS neuronal activity.
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What are focal or partial syndromes?
Abnormal activity located to a specific region of the CNS. Often associated with auras.
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What are generalised syndromes?
Activity in both hemispheres. Not associated with auras.
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What are idiopathic syndromes?
Mostly genetic in origin. A structural cause cannot be found.
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What are symptomatic syndromes?
There is an associated neurological disturbance e.g. damage from a stroke, head trauma, tumour etc.
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What is an EEG recording?
Measurement of brain electrical activity by an array of pairs of electrodes placed on the scalp. Measures predominantly cortical neuron activity.
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What is the difference between alpha rhythm and beta waves?
Alpha rhythm (8-13Hz) is characteristic of a relaxed, wakeful state and beta waves (13-30Hz) show a high degree of focused mental activity.
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What mutations are associated with idiopathic epilepsy syndromes?
Inherited mutations in sodium channels.
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What is a common finding of sodium channel mutations?
They cause a slowing of inactivation due to a change of inactivatio gating leading to a persistent current.
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By what mechanisms can Na channel mutations cause excessive firing?
Causing perisistent neuronal firing leading to hyperexcitability and cell death, loss of function in inhibitory interneurons leading to more excitation from the output neurons.
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What causes benign neonatal familial convulsions (BNFC)?
Inherited mutations in an ACh sensitve potassium channel (M-current channel).
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How is BNFC characterised?
Recurent brief generalised seizures that start on 4th day of life and cease after 1-3 months. Infants develop normally but are at a higher risk (6-13% increase) of generalised epilepsy later in life.
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What happens when muscarinic ACh receptors are stimulated?
Stimulation inhibits M-current, a potassium current. The reduction of this current increases neuron excitability.
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What is M-current?
A voltage activated K current. The current increases slowly during trains of APs and depresses neuronal excitability (firing frequency adaptation).
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What subunits make up M-current channels?
M-current channels are heteromultimers of KCNQ2 and KCNQ3 subunits.
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What causes BNFC?
Inherited mutations in KCNQ2 or KCNQ3 reducing M-current amplitude by 20-30% leading to neuronal hyperexcitability.
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What is multiple sclerosis (MS)?
An autoimmune disease that leads to damage to myelin or oligodendrocytes of myelinated CNS neurons.
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What are the classical symptoms?
Blurred vision, muscle weakness, muscle spasms and loss of sensation and most complain of fatigue and depression.
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What does demyelination do to the axon?
Increases Cm and decreases Rm this causes length constants to shorten (current leaks out faster) and time constants larger (more current required for membrane depolarisation).
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What can happen to the ion channels in MS?
They may redistribute along the axon in completely demyelinated regions so the axon essentially has the properties of an unmyelinated axon.
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When does total conduction block occur?
If current from a healthy node is not sufficient to depolarise neighboruing nodes to threshold potential. Current leaks out before it reaches an active node.
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What other effects can demyelination have?
APs have longer duration affecting refractoriness so APs are blocked at high frequencies, axons are more prone to fire spontaneous APs and excitability can be increased causing ectopically generated APs.
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How does demyelination lead to cross talk?
Reduced insulatio between axons means depolarisation in one axon can depolarise a neighbouring axon. The resulting AP propagates in both directions.
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Card 2

Front

What are focal or partial syndromes?

Back

Abnormal activity located to a specific region of the CNS. Often associated with auras.

Card 3

Front

What are generalised syndromes?

Back

Preview of the front of card 3

Card 4

Front

What are idiopathic syndromes?

Back

Preview of the front of card 4

Card 5

Front

What are symptomatic syndromes?

Back

Preview of the front of card 5
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