EEG - childhood absence seizures Flashcards
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
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
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)
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
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
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)
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
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