Sleep Physiology Flashcards
What is sleep?
Sleep is a behavioural state characterised by decreased awareness of the external environment, decreased reactivity to stimuli but with capability to rapidly return to wakefulness –> differentiates sleep from a comatose state
What are some of the purposes of sleep?
The purpose of sleep is significant for health and survival, learning, brain development (toddlers/babies 80% of sleep is REM; compared to adults at only 20%), repair and maintenance, clearance of metabolites (from the brain), energy preservation (although it is not as significant in humans) and may have at some point in history been a mechanism to avoid nocturnal hazards.
How common are sleep problems in australians? What are some common sleep problems?
Sleep Problems affect over 1.5 million Australians and include conditions such as
- Obstructive Sleep Apnoea (4.7%) - Insomnia (3%) - Restless leg Syndrome (1.2%)
Explain the principles of Polysomnography.
Polysomnography (PSG) is a method used to evaluate sleep and involves monitoring by EEG (measures brainwaves), EOG (measure eye movments) and EMG (measures muscle activity) as well as other signals to determine if someone is awake or not such as video, ECG, spO2, respiratory movements, nasal air flow, limb EMG, diaphragm EMG, transcutaneous CO2, oesophageal pressure etc.
What is the difference between REM and non-REM sleep?
While an individual is awake there are eye movements, high levels of muscle activity and high frequency EEG.
During Non-REM Sleep (Stage 1 & 2) there are no eye movements, relatively high muscle activity and lower frequency EEG. Non-REM Stage 3 (SWS) is the same but shows variable levels of muscle activity.
–> less active (slower) EEG and with relatively more muscle activity - stable/quiet
REM sleep shows rapid eye movements, low levels of muscle activity and higher frequency EEG.
–> ‘Active’ EEG and eye movements but skeletal muscle atonia (stops you acting out dreams) - unstable/active
What are some of the physiological changes during sleep pertaining to control of breathing?
Cerebral cortex, stretch receptors in the lungs and joints, central and peripheral chemoreceptors act while awake but during sleep, there is no longer a drive from the brain or muscle activity mechanisms to drive breathing and so it is promarily driving by chemoreceptors so that pH, O2 and CO2 are maintained.
What are some of the physiological changes during sleep pertaining to respiratory changes?
- Wakefulness drive
- Behavioural influences
- Down-regulation of respiratory control mechanisms (upper airway muscles, respiratory muscles and reflexes and chemosensitivity)
Ventilation falls at sleep onset and CO2 rises until a new sleep set-point is reached
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- Lower HR (particularly during NREM sleep)
- Lower BP
- Reduces CO
- Overall metabolic activity decreases markedly during sleep
- -> sleep instigated component (at sleep onset)
- -> circadian component (although not for BP)
What are some of the physiological changes during sleep pertaining to respiratory changes?
- Wakefulness drive
- Behavioural influences
- Down-regulation of respiratory control mechanisms (upper airway muscles, respiratory muscles and reflexes and chemosensitivity)
Ventilation falls at sleep onset and CO2 rises until a new sleep set-point is reached
What are some of the physiological changes during sleep pertaining to cardiovascular changes?
- Lower HR (particularly during NREM sleep)
- Lower BP
- Reduces CO
- Overall metabolic activity decreases markedly during sleep
- -> sleep instigated component (at sleep onset)
- -> circadian component (although not for BP)
What is an arousal from sleep and what are the effect of them on human physiology?
- arousals can occur during the night and are normal and often not remembered by the individual.
- arousals are longer than 3 seconds in duration
There are conflicting theories as to why arousals occur:
- arousals from sleep produce vigorous CV and respiratory activation
- homeostatic (switching back on the downregulated control mechanisms) vs. reflex activation
- evidence supports a ‘waking reflex’
- adaptive reflex response to arousal providing an evolutionary advantage
- -> however frequent arousals can cause Obstructive Sleep Apnoea (OSA) resulting in little to no REM sleep.
Explain obstructive sleep apnoea
- Results in minimal to no REM sleep due to a large decrease in oxygen saturations
- It is the number of arousals and the lack of oxygen saturation that lead to the concerns surrounding OSA.
- When Severe (>30 events/hour)
- -> Increased risk of motor vehicle (and workplace) accidents
- -> higher mortality
- -> higher risk of stroke
- -> higher risk of CVD
How is sleep regulated?
The Two Process Model of Sleep
- Homeostatic Process (Process S)
- Circadian Process (Process C)
- typically the drive to sleep is at its lowest first thing in the morning after finishing sleep
- When the two lines are as far away from each other, sleep typically occurs.
What are circadian rhythms?
Circadian: around a day
- Regular changes that occur in the course of a day include BP, urine production, cortisol levels, core body temperature, sleep-wake
- Most are controlled by the body’s biological clock - suprachiasmatic nucleus (SCN)
- Zeitgeibers (‘time givers’) act as external cues
- -> light is a powerful zeitgeiber; it inhibits the CSN and a lack of light increases melatonin levels –> sleep promoting hormone
What is Physiological process underpinning the drive to sleep?
The Physiological process underpinning the drive to sleep may be:
- Metabolite/toxin clearance?
- -> increase of metabolites in the brain, which sleep will allow to clear
