Neural mechanism of sleep/arousal

Question 1

Brain Stem Reticular Activating System (RAS)

Answer 1

Set of nuclei in the brain stem that sends fibers to the cortex with modulatory neurotransmitters

Question 2

MRF in cats

Answer 2

Medial reticular formation

in cats (asleep) MRF was activated. Effect:
- More high freq EEG (gamma)
- Firing rates variable
- Oscillations go up (more high freq)
- Synchrony goes up

More like awake EEG when stimulated

Question 3

Thalamus

Answer 3

Gates information from senses to cortex (gating agent)

Brainstem modulates this gating function, allows shutdown of information flow

Question 4

Thalamic relay cells

Answer 4

send sensory info to the cortex, But the reticular nucleus of the thalamus inhibits this (decrease in sensation)

The MRF can inhibit that inhibition (- x - = +) causing stronger input from the senses

Question 5

Thalamo-cortico oscillations

Answer 5

The cortex, thalamus and the RNT form a reverberatory circuit that’s generating different rhythms (loop w fb). This can get into oscillatory state, where oscillations get slow and its difficult for sensory info to get through

This slow flow of oscillations is disrupted by the MRF (activity back to high)

Question 6

3 functions of sleep/arousal by brainstem/MRF

Answer 6

1. act on cortes directly (neurotransmitters)
2. Disinhibit inhibitory nRT
3. Disrupt slow oscillatory flow of the thalamus