Circadian Rhythms

    Cards (12)

    • Biological rhythms

      Distinct patterns of change in body activities which conform to cyclical time periods. Biological rhythms are influenced by internal body clocks (endogenous pacemakers) and external changes to the environment (exogenous zeitgebers).
    • Circadian Rhythms 

      Biological rhythms subject to a 24 hour cycle which regulate a number of bodily processes.
    • What are circadian rhythms and how do they work?

      Biological rhythms that follow a 24-hour cycle, which regulate sleeping and feeding patterns, as well as core body temperature, hormone/urine production and other biological functions.
    • What role does melatonin play in circadian rhythms?
      • Melatonin, produced in the pineal gland chemically causes drowsiness and lowers body temperature, allowing us to sleep.
    • Where is the circadian clock located?
      In the suprachiasmatic nucleus (SCN), which is in the brain's hypothalamus.
    • How does light influence our circadian rhythm?
      Light-sensitive cells in our eyes send messages to the SCN, which uses this information to manage our sleep-wake cycle.
    • Body temperature is another circadian rhythm. Human body temperature is at its lowest in the early hours of the morning and at its highest in the early evening. Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning.
    • AO3 - practical application to shift work
      Shift work has been found to lead to desynchronisation of circadian rhythms and can lead to adverse cognitive and physiological effects. Research has shown that shift workers suffer a concentration lapse at 6am, increasing the likelihood of accidents. They are also 3x more likely to suffer from heart disease as a result of the stress of adjusting to sleep-wake cycles. This research has many economic implications in terms of maintaining worker productivity and preventing accidents in the workplace.
    • AO3 - application to pharmacokinetics
      By understanding circadian rhythms and their impact on health, for example using the knowledge that the risk of heart attack is greatest early in the morning, it can help determine the best time to administer drugs. We can therefore maximise the efficacy of drugs by looking at peak times for administration and dosage in relation to circadian rhythms.
    • AO3 - research support
      Siffre spent 2 months in caves, deprived of light and sound, determining that his circadian rhythm remained between 24-25 hours.
      Further research from participants living in WW2 bunkers for four weeks found the sleep-wake cycle lasted just under 25 hours, concluding that the body's internal clock in the absence of exogenous zeitgebers is 24-25 hours.
    • Counterpoint for case study evidence
      The Siffre study, and others were only conducted on a handful of people and, consequently, it is impossible to generalise these results to an entire population, as there may be individual differences in the participants which could account for their response to changes in the sleep/wake cycle. For example, Czeisler has found evidence to show cycles can vary by as much as 13-65 hours. This suggests results cannot be generalised from small samples, as factors such as age and gender may also impact our circadian cycles.
    • Limitation - poor control in studies
      In the cave studies, the exposure to artificial lights were not controlled. Furthermore, research by Czeisler found that dim artificial lighting could also adjust the circadian rhythm, which means the results from the original studies may lack validity. Additionally, there are practical implications in Czeisler's research when it comes to the use of electronic devices, as it made us aware of the impact of artificial lighting on our circadian rhythms.