96 - Sleep Physiology Flashcards
What is sleep?
Behavioural state.
Decreased awareness of external stimuli.
Can rapidly return to wakefulness.
Why do we sleep? 1 2 3 4 5 6
- Learning
- Brain development
- Repair and maintenance
- Clearance of metabolites
- Energy preservation?
- Avoid nocturnal hazards?
Number of Australians who might have a sleep disorder
~1.5 million
Signals used for polysomnography
1
2
3
EOG - electrooculography
EMG - Electromyography
EEG - Electroencephalography
Things that can also be measured in polysomnography
Video.
SpO2
Nasal airflow
Things that can also be measured in polysomnography
Video.
SpO2
Nasal airflow
Graphical representation of sleep
Hypnogram
Main features of wakefulness on a polysomnograph
Eye movements.
High levels of muscular activity
High frequency EEG
Main features of stage 1 and 2 non-REM sleep
No eye movements
Relatively high muscle activity
Lower frequency EEG
Main features of stage 1 and 2 non-REM sleep
No eye movements
Relatively high muscle activity
Lower frequency EEG
Main features of stage 3 non-REM sleep
No eye movements
Variable levels of muscle activity
Low frequency EEG (‘slow wave sleep’)
Main features of REM sleep
Rapid eye movements.
Low levels of muscle activity
Higher frequency of EEG
Main features of REM sleep
Rapid eye movements.
Low levels of muscle activity
Higher frequency of EEG
Effect of sleep on breathing
1
2
3 a b c d
• Lose wakefulness drive • Behavioural influences • Down-regulation of respiratory control mechanisms: –upper airway muscles –respiratory muscles –respiratory reflexes –chemosensitivity
Ventilation when asleep
Ventilation Falls At Sleep Onset And CO2 Rises Until A New Sleep Set-Point Is Reached
Cardiovascular changes during sleep 1 2 3 4
- Lower HR (particularly during NREM sleep)
- Lower BP (at sleep onset)
- Reduced cardiac output
- Overall metabolic activity decreases markedly during sleep
What happens in an arousal during sleep?
1
2
3
Increased EEG, EMG frequency.
Increase ventilation, diaphragmatic activity.
Increase HR, BP
What happens in an arousal during sleep?
1
2
3
Increased EEG, EMG frequency.
Increase ventilation, diaphragmatic activity.
Increase HR, BP
What causes physiological responses to arousals during sleep?
Unclear.
Might be that systems suppressed when asleep are just starting up again.
Might be a waking reflex, to be able to respond to a dangerous stimulus waking you up from sleep.
Number of arousals in severe obstructive sleep apnoea
Over 30/hour
Dangers of severe OSA
1
2
3
1) Increased risk of car accident
2) Higher risk of stroke
3) Higher risk of CVD
Body part which regulates circadian rhythm
Suprachiasmatic nucleus
Body part which regulates circadian rhythm
Suprachiasmatic nucleus
Name for an external cue that can influence circadian rhythm
Zeitgeiber
Example of a very strong zeitgeiber for sleep
Light
Effect of light on circadian rhythm
Light inhibits the SCN
Lack of light increases melatonin levels (released from pineal gland)
Melatonin promotes sleep
Effect of light on circadian rhythm
1
2
3
Light inhibits the SCN
Lack of light increases melatonin levels (released from pineal gland)
Melatonin promotes sleep
*Two-process model of sleep
TWO PROCESS MODEL
*Two-process model of sleep
TWO PROCESS MODEL
Circadian process tries to keep us awake.
Homeostatic process tries to get us to sleep
*Two-process model of sleep
TWO PROCESS MODEL
Circadian process tries to keep us awake.
Homeostatic process tries to get us to sleep
What physiological process might underlie the desire to sleep?
Metabolite/toxin clearance.
Sleeping mice had a greater clearance of beta-amyloid than mice who were awake or sedated.
Danger of chronic sleep restriction
Performance in tasks becomes increasingly impaired, but subjective perception of performance normalises.
Therefore become less able to judge performance.
Three functional systems which might control sleep
1) Arousal systems
2) Sleep promoting system
3) Orexin neurons
Where are arousal systems located?
located in multiple areas within pons/midbrain
Where is the sleep-promoting system located?
includes VLPO (ventrolateral pre-optic nucleus)
Where are orexin neurons located?
located in the hypothalamus – project onto arousal systems (stimulate)
Three functional systems which might control sleep
1) Arousal systems (maintains wakefulness)
2) Sleep promoting system (inhibits both orexin and arousal systems)
3) Orexin neurons (stabilise wakefulness)
Where are arousal systems located?
Located in multiple areas within pons/midbrain
Where is the sleep-promoting system located?
Includes VLPO (ventrolateral pre-optic nucleus)
Where are orexin neurons located?
Located in the hypothalamus – project onto arousal systems (stimulate)
Part of brain damaged in narcolepsy
Orexin neurons
Part of brain damaged in narcolepsy
Orexin neurons
