circadian rhythms Flashcards
biological rhythms
- patterns of change in the body that follow a cyclical time period
3 main biological rhythms
circadian
ultradian
infradian
Flashcard 2: Q: Name three types of circadian rhythms.
Sleep/wake cycle
Body temperature
Hormones
Flashcard 1: Q: What are circadian rhythms?
Biological rhythm recurring every 24 hours
Set and reset by environmental light levels
Flashcard 4: Q: What time is body temperature lowest and highest?
Lowest at 4:30 am (~36°C)
Highest around 6 pm (~38°C)
Flashcard 5: Q: What is the “post-lunch dip” in body temperature?
Afternoon drop in body temperature
Causes tiredness, even without eating
Linked to afternoon siestas in some cultures
Flashcard 6: Q: How do cortisol levels follow a circadian rhythm?
Lowest around midnight
Peaks around 6 am
Helps with stress and alertness
Flashcard 7: Q: How does melatonin follow a circadian rhythm?
Peaks at midnight
Induces sleepiness
Stays low during the day
Micheal siffre
Michael Siffre spent long periods underground with no exposure to daylight, radios, or clocks to investigate his brain’s rhythms.
He woke, ate, and slept based on how he felt, without external time cues.
On one occasion, Siffre spent 6 months in a Texan cave in 1975.
During this time, he measured his vital signs (e.g., heart rate) to study his circadian rhythm.
His sleep-wake cycle adjusted to a 24-hour day, but his circadian rhythm averaged 25 hours.
Occasionally, his cycle changed dramatically, extending up to 48 hours.
ao3 strength
P – Research supports the existence of circadian rhythms.
E – Wever and Aschoff studied participants in a WWII bunker for four weeks, finding a sleep/wake cycle lasting just under 25 hours, indicating that circadian rhythms are influenced by exogenous zeitgebers like light and meal times.
E – Additionally, Folkard et al. (1977) found that memory recall and comprehension were better in the afternoon, when core body temperature was higher, compared to the morning.
L – This research validates the concept of circadian rhythms, suggesting their role in both the sleep/wake cycle and body temperature regulation.
ao3 limitation
P – There are issues with the studies supporting circadian rhythms.
E – Siffre’s study involved only himself, and the studies by Folkard, Wever, and Aschoff included just a few participants.
E – As a result, these findings cannot be generalized to the broader population, as individual differences may make the participants’ sleep/wake cycles atypical.
L – This indicates a lack of external validity, as factors like age and gender can significantly influence circadian rhythms.
(stretch) – Nevertheless, Siffre’s use of the experimental method allows for causal inferences.
ao3 strength
P – A key strength of circadian rhythm research is its practical applications for drug treatments.
E – Understanding circadian rhythms helps identify optimal times for administering medications.
E – For instance, since the risk of heart attack is highest in the early morning, drugs can be taken at night and activated when most effective.
L – This highlights the research’s practical utility in timing drug doses for various medications, including cardiovascular drugs.
ao3 weakness
P – There were methodological issues with the original studies, including Siffre’s.
E – In the cave studies, exposure to artificial lights like torches and phones was not controlled.
E – It was assumed that only natural light influences biological rhythms, but research by Czeisler showed that dim artificial lighting can adjust circadian rhythms to between 22 and 28 hours.
L – This is a weakness as it suggests the original studies may lack internal validity, indicating that the sleep/wake cycle could vary more than previously reported.
