Lecture 30: Chronobiology II Flashcards
sleep
What happens if someone does not sleep for many days?
the magnitude of sleep deprivation effect is the same as….
What happens at 12 to 21 hrs of wakefulness ?
What happens at ~ 17 hrs wakefulness ?
What happens at 21-25 hrs wakefulness ?
What happens from 25 hrs onwards ?
True/ false : We sleep with a daily biological rhythm
Die
The magnitude of blood alcohol concentration effect. (Increase sleep deprivation = increased blood alc conc.)
Performance drops greatly
Same as classified as too drunk to drive
Double performance impairment
Performance gets better -> biological clock wakes you up
True
What controls sleep-wake cycle and how does it do it
Sleep “homéostat” -> longer stay awake, more propensity to go to sleep : sleep gene (sleep wake history)
Circadian clock -> sometimes drive sleep, sometimes prevent sleep : biological time : clock genes
What is forced desynchrony used for
comprehend circadian clock’s influence on wakefulness and sleep
-> separating your wakefulness duration effects from your circadian drive for sleep or wakefulness
Why is it harder to sleep at 7am compared to 11pm?
Circadian drive of wakefulness is important
11pm: biological clock -> encouraging sleep through the night
7am: even if well rested, biological clock -> only sleep for a couple 100s minutes before waking up
True/false: All organisms have biological clocks
True
How is the human circadian clock trained ?
What did the experiment with a guy kept in lab for 87 days show about the human endogenous period?
SCN -> trained by light & adjusted on a daily basis by light to 24 hrs.
Constant dim light shifted circadian rhythm (wake up slightly later each day) -> show it is longer than 24 hrs
What light is important to train biological clock and why?
Morning light
- phase advancing light -> need to train clock on daily basis.
- Advances humans to earlier time zone -> human circadian clock >24hrs
What does a phase response curve show
The different effects on light at different times of the day
- Phase advance : (+) values
- Phase delay: (-) values
What does morning light and evening light to
Advances the clock
Delays the clock
Are eyes needed to train the circadian clock?
What did rodless conless mice experiments show when a single light pulse was shone?
What kind of photoreceptor of the eye are responsible for light entrainment
Yes
Phase shifting
Intrinsically Photoreceptive Retinal Ganglionic Cells
Melanopsin and intrinsically photoreceptive retinal ganglion cell
A photo pigment possessed by a part of a subset of photoreceptive cells called intrinsically photoreceptive retinal ganglion cell
Sensitive to blue end of spectrum
Key for light entrainment by circadian clock
Circadian photo reception is blocked if this is blocked
What shifts/entrains biological clock maximally ?
What is sleep like for blind people?
Blue light from devices and modern LED light
Blue light of maximum wavelength
Have free running sleep disorder -> cannot adjust biological clock to 24hr day
Shifts the clock and sleep later
Jet lag
Time zone travel outside of immediate adaptation/entrainment range
Operate at times when circadian clock encourages sleep.
Requires a number of cycle to adapt even with ‘ideal’ light exposure timing
When travelling eastwards,
When travelling westwards,
Phase advance
Phase delay
Why is it harder to adapt to time zones on the east (phase advance) compared to the west (phase delay)
On the human phase response curve, you can delay maximally 3 hours per day on the human phase response curve whereas you can only advance 1.5 hours per day maximally.
Therefore, harder to adjust to earlier time zone compared to later time zone
Ways to reduce jet-lag
Is chronic jet lag fatal?
Maximise light phase shifting
[light -> eye -> SCN -> pineal gland : melatonin feedback to SCN by Mel receptors]
Mouse experiment -> mice that were phase advanced die more than phase delayed mice who die more than control.
- shows difficult to shift to different time zones & longer health consequences if continually do it for long time
What is circadian rhythm of a person in the Antarctic summer compared to winter
What did studies in European hospitals show when patients were exposed to increased daylight lighting?
What is the importance of morning light
Summer: sleep and wake at same time each day
Winter (no access to light): circadian disruption -> disturbance to one’s circadian rhythm
Patients spent lesser time in the hospital. Discharged later
To train our circadian clocks and improve health outcomes
Explain why night time light would be problematic
Leading to phase delay so circadian clocks will be trained to later time zones
Immediate and longer term consequences of a disrupted clock
Immediate
- sleep timing and mood (seasonal affected disorder - treated with morning light) problems
Longer term
- fatigue
- impaired wound healing, immune function, metabolic response to food
- diabetes, heart disease, cancer
What is sleep like in older people
Weaker and less robust
- less powerful electrical firing & rhythms from SCN.
- lens gets more yellow/orange as you get older -> filter blue light
What did a strong sleep/wake cycle in people with dementia show
Rhythmic activity,
Improved sleep/wake cycle
Reduced depression & anxiety
Slowed disease progression
Improved sleep
Describe why someone partying to 3am on a Friday and Saturday night makes them feel horrible on a Monday morning
PHASE RESPONSE CURVE
Friday night: party -> light - induced phase delays (light in evening/night) delay to later time zone
Saturday morning -> no light induces phase advance (wake up in afternoon), no phase advance (avoid morning light - not getting it)
Saturday night -> light - induced phase delays (party) (Lots of night light exposure)
Sunday morning -> no light-induced phase advances (sleep in)
Monday -> Australia time zone (Phase delay so much and now have to advance back to NZ time)
