Circadian Rhythms Flashcards
(10 cards)
What are Circadian Rhythms?
biological rhythms that last around 24 hours. They regulate processes like the sleep-wake cycle and body temperature. These rhythms are governed by endogenous pacemakers (like the suprachiasmatic nucleus, SCN) but are also influenced by exogenous zeitgebers (like light).
What is the sleep-wake cycle?
The SCN in the hypothalamus detects light via the eyes and adjusts melatonin production in the pineal gland. Melatonin levels increase at night to promote sleep and decrease in daylight to promote wakefulness. This rhythm can be disrupted by shift work or jet lag, showing the importance of synchronisation with external cues.
What are Exogenous Zeitgebers?
external environmental cues that reset biological clocks. Light is the most powerful zeitgeber and synchronises the SCN to the 24-hour day. Other zeitgebers include social cues such as mealtimes or activity patterns. These help align internal rhythms with the external world.
What are Endogenous Pacemakers?
internal biological clocks that regulate rhythms like the sleep-wake cycle. The main pacemaker is the SCN, located in the hypothalamus, which receives light signals from the retina. The SCN sends signals to the pineal gland to release melatonin at night, inducing sleep.
Siffre study
Siffre spent 6 months in a cave without natural light or cues, yet his sleep-wake cycle remained close to 24 hours. This supports the existence of an internal biological clock. However, his rhythm did slightly drift, highlighting the importance of external cues like light in resetting the cycle. The findings demonstrate that circadian rhythms are internally regulated but need entrainment to keep to 24 hr cycle
Aschoff & Wever
placed participants in a bunker with no natural light, clocks, or external cues for several weeks to investigate the role of endogenous pacemakers. Most participants maintained a sleep–wake cycle of around 24–25 hours, although some extended to 29 hours = supports the idea of a built-in circadian rhythm regulated by internal biological clocks, but shows that without external zeitgebers like light, the cycle becomes slightly longer = highlights the importance of exogenous factors in resetting our internal clock.
weakness- low generalisability
studies often rely on small sample sizes- Siffre conducted study on his own internal biological clock and reported differences as he aged = slower clock at 60 yrs. these findings are highly individualised, leading to reduced population validity = cannot draw broad conclusions
strength- real world application
promotes healthier sleep habits- studies on circadian rhythms have shown exposure to blue light can disrupt sleep cycles = led to recommendations for reducing blue light exposure for better sleep cycles. by understanding this, people can make informed decisions to limit devices before sleep for good wellbeing, which demonstates practical value = enhances public health
weakness- individual differences
There are significant individual differences in circadian cycles, with some people naturally rising earlier (larks) and others later (owls). These variations suggest that a single, universal pattern may not apply to everyone. This reduces the generalisability of findings and suggests personalised approaches may be necessary when applying research to work or health.
strength- highly controlled and objective methods.
Studies like those by Siffre and Aschoff & Wever were conducted in environments where variables such as light, temperature, and external time cues were strictly controlled.
Additionally, modern studies often use devices like EEGs and body temperature monitoring, which provide precise and quantifiable data. This scientific approach increases the internal validity of the findings and strengthens the claim that circadian rhythms can be studied in a replicable way.
