thalamocortical physiology Flashcards
What does the EEG measure
collective activity of large neurons near the surface of the brain.
how does the thalamus contribute to EEG measurements
The contribution of thalamus to EEG recording is indirectly- due to thalamocortical connections.
What are thalamic relay neurons
Cells located in the thalamus that receive an input from a sensory system and relay that information to cortex via
excitatory glutamatergic synapses onto pyramidal cortical neurons with soma in layer IV of cortex
thalamic relay neuron activity when awake
They receive little inhibitory input and their membrane potential rests at -55 mV. When these cells are depolarized under these conditions the neurons fire a series of action potentials at high frequency
thalamic relay neuron activity when asleep
When animal is asleep in slow wave stage, thalamic reticular neurons inhibit TR neurons by releasing GABA. Resting membrane potential is at -85mV and the TR neurons respond to hyperpolarization with Ca spikes firing at a frequency of 3Hz (delta wave frequency), and riding on top of the spikes are action potentials at 3Hz
What channel plays a role in the slow Ca spike seen in thalamic relay neurons during sleep
T-type Ca channel- Activated by hyperpolarization. Inactivation gate opens and the Ca channel generates Ca spikes at a frequency of 3 Hz.
describe how the thalamus contributes to EEG measurements
Thalamic reticular cells hyperpolarize thalamic relay neurons > T-type Ca channels in thalamic relay neurons open > TR neurons generate Ca spikes at 3Hz and action potential bursts > TR neurons stimulate cortical pyramidal cells > cortical pyramidal cells fire at 3 Hz (delta freqency) > slow wave EEG recorded
EEG in absence epilepsy
resembles slow waves of stage IV sleep (delta waves, 3 Hz). Caused by oscillations of corticothalamic circuit
How is absence epilepsy induced in mice genetically
Mutations in T-type Ca channel gene that alter the voltage dependence of the inactivation gate makes it possible for the thalamic relay neurons to fire slow Ca spikes at depolarized resting potentials (-60mV). Conversely, these seizures cant be induced in mice where the gene for the T-type Ca channel has been removed.
Actions of ethosuximide and valproic acid
Block T-type Ca channels and thus are clinically effective against absence epilepsy
What regulates the thalamocortical circuits
Axons ascending from brain stem from cholinergic, noradrenergic and serotonergic neurons
What causes awakening from sleep?
Stimulation of cholinergic neurons in reticular activating system interrupts slow waves and awakens the animal
