Thalamocortical physiology

Question 1

What is the activity state of thalamic relay neurons when the animal is awake?

Answer 1

disinhibited. Depolarized TR neurons –> high frequency APs –> high rate of cortical cell firing recorded on EEG

Question 2

What is the activity state of thalamic relay neurons when the animal is asleep?

Answer 2

Inhibited by GABA from thalamic reticular neurons –> “slow wave” stage.

Question 3

How does the thalamus affect EEG recordings?

Answer 3

Thalamus is the “gateway” to the cortex for sensory information. Thalamic relay neuron activity –> layer 4 pyramidal neuron activity –> EEG recordings

Question 4

What is the resting membrane potential of a thalamic relay cell during slow wave sleep?

Answer 4

-85 mV

Question 5

Describe TR cell action potentials during slow wave sleep

Answer 5

AP “bursts” riding on top of a Ca spike. Frequency = 3 Hz (delta frequency)

Question 6

What is the resting membrane potential for thalamic relay neurons while awake?

Answer 6

-55 mV

Question 7

What is the channel responsible for the slow Ca spike?

Answer 7

T-type Ca channel

Depolarization –> inactivation
Hyperpolarization (via thalamic reticular neurons) –> opened inactivation gates –> Ca spikes at 3 Hz

Question 8

What is the result of mutation in the T-type Ca channels?

Answer 8

mutation –> altered voltage dependence of inactivation gate –> TR neurons fire slow Ca spikes at DEpolarization potentials (-60 mV) –> spontaneous absence seizures

Question 9

What drugs would you use to treat absence seizures?

Answer 9

T-type Ca channel blockers:

Ethosuximide, Valproic acid

Question 10

What is the mechanism of awakening an animal?

Answer 10

stimulation of cholinergic neurons in reticular activating system –> awakening, interruption of slow waves in EEG