AQA PSYA3 - Biological Rhythms - Pacemakers & Zeitgebers

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Biological rhythms = regular rhythmic changes in biological and psychological processes.

  • They generally coincide with things in the environment, such as humans sleeping at night when it activity is difficult
  • Regulated by pacemakers and zeitgebers:
    • Endogenous pacemakers = internal biological clocks
    • Exogenous zeitgebers = external environmental influences (remember ex- as external)

Types of biological rhythms:

  • Circadian: 24 hours. 
    • Eg. Sleep-wake cycle, changes in body temperature.
  • Infradian: Longer than 24 hours
    • Eg. Menstrual cycle, hibernation in animals, SAD (seasonal affective disorder).
  • Ultradian: Less than 24 hours
    • Eg. Alternation between sleep stages

Circadian rhythms and how they are regulated:

  • The sleep-wake cycle is regulated with both exogenous zeitgebers and endogenous pacemakers.
  • Endogenous pacemakers: The SCN (suprachiasmatic nucleus) is a bundle of nerves in the hypothalamus. It is connected to the retina in the eye, so when the retina is exposed to light, signals are sent to the SCN. The SCN is also connected to the pineal gland. The pineal gland converts serotonin (neurotransmitter) into melatonin (hormone that plays a role in inducing sleep). The SCN controls the release of melatonin from the pineal gland, so when the retina is receiving low levels of light, the SCN signals the pineal gland to increase the release of melatonin, and when light levels rise, the pineal gland releases less melatonin. Therefore it plays a large role in regulating the circadian rhythm. (Less Light = More Melatonin)
    • Menaker et al (1978) --> cut the SCN in hamsters. Their circadian rhythms were disrupted. This shows that the SCN plays a large role as an endogenous pacemaker (although there are issues with extrapolating results from research on animals).
    • Research has shown that melatonin levels increase in darkness and decrease in light.
    • Further evidence in shown in the fact that this pattern is seen in people all over the world with different lifestyles, suggesting that it's nature rather than nuture.
  • Exogenous zeitgebers: Exogenous zeitgebers in relation to circadian rhythms include noise levels, eating patterns and temperature, however the…

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