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Flashcards in Circadian Rhythms Deck (11)
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What is a circadian rhythm

Any cycle that lasts for 24 hours
Eg sleep wake cycle
Body temperature
Hormone production


Explain the sleep wake cycle

Light and dark provide signals about when we should be awake and we should be asleep

Our strongest sleep drive (want to sleep) occurs between 2 - 4 am and 1 - 3 pm (post lunch). Sleepiness is less intense with circadian dips if we have had enough sleep the night before.


What is another thing that affects our sleep wake cycle

Homeostasis also controls our need to sleep. This is why we get more tired as the number of hours we have been awake increases.

control allow us to sleep during the night and be awake during the day.
Effect of day light - important effect on when we feel drowsy and awake


Explain siffres study

Spent several extended periods underground to study. Effect of his biological rhythm

Deprived of exposure to natural light
Spent two months in caves of southern alps in September
But believed it was mid august

Free running biological rhythm settled to beyond 24 hours
And can be entrained by exogenous zeitegabers


Explain simon folkard study

Studies a group of 12 people
Agreed to live in dark cave for 3 weeks
When clock said 11:45pm they went to bed
Raised when it said 7:45 am
Researchers gradually sped up clock
24 hour day -> 22 hour day
Not one participant comfortably adjusted
Free running circadian rhythm not overidden enough by changes in enviroment


How is hormone production a circadian rhythm

Melatonin is produced and released from the pineal gland.
Melatonin levels peak during the hours of darkness.

By activating synapses in the brain, melatonin encourages feelings of sleep. When it is dark, more melatonin is produced, and when it is light, less melatonin is produced.


What is the best indicator of the sleep/ wake cycle and explain it

Body temperature
Lowest about 4 am
Highest at 6pm
36 degrees in morning + 2 degrees
38 degrees in the evening
Sleep occurs when body temp drops


What is a strength of circadian rhythms (practical application)

Shift work
Bolvin et al
Shift workers experience lapse concentration at 6am so mistakes and accidents - more likely

Has economic implications
In how to manage worker productivity and safety
Shift change OVERS before circadian trough - less mistakes


What is another srength of research into circadian rhythms (drug treatments)

Practical applications in drug treatments
CRS coordinate basic processes such as heart rate and hormone levels
Implication of pharmacokinetics
Research shows times during the day when drugs more effective
Research into circadian rhythms - real life medical benefits


What is a limitation of circadian rhythms (small samples

common use of case studies and small samples.

Siffre’s research used small groups or individual participants.
Participants may not be representative of the wider population and results cannot be generalised
not everyone’s circadian rhythms are the same.

Siffre observed that his internal clock ticked much more slowly at 60 than when he was younger.
even when the same person is involved, there are factors that may prevent conclusions being drawn.


What is another limitation of circadian rhythms (poor contro)

Deprived natural light
Access to artificial light

Siffre had lamp from when he woke up to bed
Assumed - artificial lighting - no effect
Czeisler et al adjusted circadian rhythms from 22 to 28 hours using dim lighting

Researchers ignored important confounding variables - reducing validity