EEG - childhood absence seizures Flashcards

1
Q

What does the EEG measure?

A

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
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2
Q

Why would the EEG show thalamus activity?

A

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
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3
Q

What is a delta wave?

A

“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)
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4
Q

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

A
  • 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
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5
Q

Describe the stages of sleep on the EEG

A
  • 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
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6
Q

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

A
  • excitatory, glutamate is released

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

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7
Q

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

A

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

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8
Q

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

A
  • 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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