neurobiology of sleep

Question 1

what defines sleep stages?

Answer 1

brain activity, muscle activity, and eye movements

Question 2

what are the two main processes that regulate sleep?

Answer 2

circadian and homeostatic processes

Question 3

what is homeostatic pressure

Answer 3

‘sleep debt’ - how tired you feel

Question 4

what is circadian rhythm

Answer 4

entrained 24hr rhythm of sleepiness and wakefulness

Question 5

what is ultradian rhythm

Answer 5

cycle of less than 24hrs - shorter sleep cycles of changes that occur within the circadian rhythm and nrem and rem cycles - changes in sleep depth, awakening, etc

Question 6

what is some evidence that slow wave sleep is one of the most important processes for being fully rested?

Answer 6

-babies and kids have more slow wave sleep
-slow wave sleep is more concentrated early on in the night (when we first go to bed and are tired)
- when we are kept awake for a long time and finally allowed to sleep, we go straight into slow wave sleep

Question 7

why do we say that a lot of the arousal systems in the brain are ‘redundant?’

Answer 7

because we have so many of them - waking up from sleep is so important that we need many systems so that if one is damaged, another can compensate for it

Question 8

why do we say that arousal systems are global

Answer 8

because arousal systems are networks involving many brain areas and neurotransmitters
- neurons with long axons, descending and ascending projections

Question 9

why is REM sleep unique in terms of arousal?

Answer 9

because some arousal systems are off and others are off
- we have cortical arousal in REM but muscle atonia

Question 10

why is the arousal system ascending

Answer 10

because it starts in the brainstem and goes all the cortex

upper brainstem → posterior and lateral hypothalamus → basal forebrain

Question 11

orexin

Answer 11

neurotransmitter that particularly affects motor arousal - very important for REM sleep regulation. Orexin projections go to the forebrain and the brainstem.

Question 12

what happens when you have a lack of orexin?

Answer 12

lack of orexin is associated with narcolepsy with cataplexy

condition where patients spontaneously enter REM sleep and lose muscle tonus during the day - sometimes happens when experiencing strong emotion

Question 13

which neurotransmitters are involved in wake -on, rem-off arousal?

Answer 13

• serotonin
• norepinphrine (high discharge in wake and low in nrem, off in rem)
• histamine (high in wake, low in nrem, off in rem)
• orexin

Question 14

which neurotransmitters are involved in wake -on, rem-on arousal

Answer 14

neurotransmitters that are high in waking and high in rem (but low in nrem)
- acetylcholine
-dopamine
-glutamate

Question 15

which area of the brain regulates sleep?

Answer 15

the ventrolateral preoptic areas in the hypothalamus (just next to the optic chiasm)

• contains sleep promoting neurons - more active in sleep (nrem and rem(
• responsive to sleep deprivation and accumulation of homeostatic pressure
• some regulating stuff is also in the median preoptic nucleus

Question 16

what is the main neurotransmitter in the ventrolateral preoptic area?

Answer 16

GABA (also the most important inhibitory neurotransmitter in the entire brain)
- inhibits wake promoting arousal circuits and is associated with sleep promoting circuits

Question 17

what is the flip flop sleep switch system?

Answer 17

describes the coordination between sleep and wake systems

both systems are always acting to inhibit each other, however, which one wins out depends on homeostatic pressure and circadian rhythms

for example:
in wake, the vlpo is inhibited by arousal systems. however, in sleep, vlpo inhibits arousal systems.

Question 18

when is orexin most positively expressed? when is it expressed the least

Answer 18

expressed the most:
- positive emotion
-social interaction
- negative emotion

expressed the least:
- awake while in pain
- sleeping just before wake
-sleeping
- after eating
- before eating
- sleep onset

Question 19

what is the difference between tonic and rhythmic patterns?

Answer 19

tonic = desynchronized
rhythmic: synchronized

Question 20

what are thalamocortical loops?

Answer 20

connections between the thalamus and the neocortex - in waking, the thalamus acts as a relay system sending info to the cortex, which is responsible for higher cognitive functions

Question 21

what do thalamocortical loops do in nrem sleep and rem sleep?

Answer 21

nrem: reduced activity
rem: activity similar to waking

Question 22

describe how thalamocortical loops play a role in sleep

Answer 22

• they have reduced activity in nrem, allowing us to maintain deep sleep
• they have increased activity in rem, allowing us to dream vividly
• they also play a role in transitioning between sleep and wake

Question 23

why is it difficult to answer the question ‘what controls sleep?’

Answer 23

because different systems control different parts of sleep and on different scales:
- circadian system
-homeostatic system
-hormonal system
-limbic system
- neocortex

Question 24

what is adenosine

Answer 24

an inhibitory neuromodulator of the central nervous system - having a bunch of adenosine in our system makes us sleepy

• blocked by caffeine
• inhibits wake promoting neurotransmitters (serotonin, acetylcholine, norepinephrine)
  -accumulates in basal forebrain with sleep debt and diminishes during sleep

Question 25

what is a coffee nap

Answer 25

idea that we can enhance the rejuvenating effects of a nap by timing it with coffee consumption (remember coffee doesn’t work right away!)A