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Flashcards in EEG - childhood absence seizures Deck (8):
1

What does the EEG measure?

the sum of lots of surface-level neurons. Essentially it only measures the cortex
*thus, to say that it is dealing with the thalamus really means it's dealing with thalamacortical projections.
*this lecture is about the thalamic relay neurons and how they excite the cortex

2

Why would the EEG show thalamus activity?

the sum of lots of surface-level neurons. Essentially it only measures the cortex
*thus, to say that it is dealing with the thalamus really means it's dealing with thalamacortical projections.
*this lecture is about the thalamic relay neurons and how they excite the cortex
*it's the delta waves and the T-type calcium channels in the thalamic relay neurons that are all-important in this lecture

3

What is a delta wave?

"slow" wave of thalamocortical action potentials that seem to ride the peak of calcium-spikes.
*very important to know delta-wave = 3Hz
*also important to recognize the deal is with T-type calcium channels (establish their own rhythms)

4

What's up with T-type calcium channels being the problem in absence seizures?

*animal studies make us suspect that T-type calcium channels that are pre-disposed to opening at more depolarized potentials (not during sleep) are involved in the absence-type seizures.
*if the mice do not have the T-type calcium channel, they don't make delta waves
*if the mice have a mutation of the channel, you can't pharmacologically induce the seizures

5

Describe the stages of sleep on the EEG

*awake, definately no delta waves
*stage I - slightly more spaced out peaks
*stage II - deeper peaks and valleys, but not spread out as much yet
*stage III - even deeper peaks and valleys and you start to see spread out peaks and valleys
*stage IV - KNOW THAT DELTA WAVES ARE HERE
*REM - more like awake than stage IV

6

Describe the synapse of the Thalamic relay neuron and the cortical pyramidal cell (or the cell in the cortex)

*excitatory, glutamate is released
*the projection from cortex back to thalamic relay neuron is also stimulatory (glutamate)

7

Describe the overall membrane potential of the thalamic relay neurons during stage IV of sleep

hyperpolarized. Camp out around -85mV
*T-type calcium channel begins calcium peak
*add's rhythmicity to the circuit
*at the peak of the calcium influx you get a high frequency of APs
*the duration of the calcium peak is about 1/3 of a second
*hyperpolarization comes from the inhibitory contacts of the reticular cell

8

Describe why the T-type calcium channel is responsible for the calcium spikes

*inactivation gate of this channel does not come out until the hyperpolarized potentials
*normally, around -85mV
*pathologically, around the -60mV range, which is in the range of the awake resting potential
*thus, in absence seizures, these kids have delta waves that are initiated by the T-type calcium channel spikes

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