Circadian rhythms

    Cards (13)

    • Rhythm refers to events that repeat themselves on a regular basis.

      Rhythms with period length of 24 hours- circadian rhythms.
    • Many physiological functions e.g. body temp, hormone secretion, hunger etc all follow a circadian rhythm.
    • Environmental light levels cause neural signals to be sent to SCN (suprachiasmatic nucleus), so circadian rhythm synchronised with daylight hours- known as PHOTOENTRAINMENT.
    • Cortisol produced when we are stressed, related to making us alert when wake up
    • Sleep- wake cycle example of circadian rhythm
      • Controlled by SCN in hypothalamus
      • Strongest sleep drive between 2-4am and 1-3pm, more intense if sleep deprived
      • This ‘free running’ internal circadian ‘clock’ maintains cycle of 24-25 hours even in absence of external cues e.g. still sleepy regardless of light
      • Disrupted by major changes e.g. shift work or jet lag
      • Homeostatic drive for sleep increases gradually throughout day, as use up energy in activity
    • Core body temperature another example of circadian rhythm
      • Lowest body temp at 4:30am of 36 and highest at 6pm of 38. Also dips between 2pm and 4pm, which explains sleepiness in afternoons
      • body temp rises in last hours of sleep, leads to alertness in morning
      • sleep occurs when temperature begins to drop
    • Hormone production another example of circadian rhythm
      • Melatonin production by pineal gland peaks during hours of darkness, promoting sleepiness.
    • + Part 1 A strength of circadian rhythms is there’s research support for the importance of light. This is demonstrated by Hughes (1977) who tested the circadian hormone release in four participants. He found after three months of continuous darkness in the Antarctic, the pattern of cortisol levels had changed from the peak being when they awoke, to now being at noon.
    • + Part 2 This tells us that daylight may be responsible for variations in circadian hormone release. An argument against this could be that other research in the arctic where participants were subject to prolonged winter darkness showed no disruption of cortisol release patterns.
    • Part 1 (temp) argued temperature more important than light in setting circadian rhythms. Buhr et al (2010) shows temperature controls our body clock rather than light. Although light could be a trigger, the suprachiasmatic nucleus shifts info on light levels into neural messages that set body’s temperature which fluctuates on 24 hour circadian rhythm. even small changes in body temp can send powerful signals to internal body clocks.
    • Part 2 (temp) Buhr et al found fluctuations in temp set timing of cells which causes organs to become active or inactive. evidence suggests temperature more important in setting circadian rhythms than light, which is an exogenous zeitgeber.
    • Part 1 (research methodology) research studies of circadian rhythms suffer from flaw when estimating ‘free-running’ cycle of human circadian rhythms. The evidence shows participants were isolated from variables that could affect their circadian rhythms, such as clocks, radios and daylight. means results could be somewhat inaccurate. However, they weren’t isolated from artificial light as it was believed this would not affect their circadian rhythms whereas daylight would.
    • Part 2 (research methodology) A criticism of this is that Czeisler found dim artificial lighting alone, may have confounded his results when studying circadian rhythms. In conclusion, the research methodology of circadian rhythms is flawed and certain variables like artificial light may have confounded the results.