Biological Rhythms

• Biological rhythms

  Patterns of change in activities within the body that have evolved in response to environmental influences
• 3 types of biological rhythms

  • circadian
  • infradian
  • ultradian
• 2 factors that govern circadian rhythms

  • endogenous pacemakers
  • exogenous zeitgebers
• endogenous pacemakers

  internal factors such as the SCN
• exogenous zeitgebers

  external factors such as light
• circadian rhythms

  Last around 24 hours, such as the sleep-wake cycle
• Michel Siffre

  spent 61 days in a cave with no natural light or way of telling the time - his sleep wake cycle set itself to 26 hours as he believed one day was longer than it was
• sleep-wake cycle

  a 24 hour cycle with typically 8 hours asleep and 16 hours awake
• exogenous zeitgeber in the sleep-wake cycle

  light
• endogenous pacemaker in the sleep-wake cycle

  SCN
• problem with Siffre’s study

  case study so idiographic and cannot be generalised to the wider population
• Aschoff & Wever (1962)

  ppts lived in a bunker for 4 weeks with no natural light - they settled into a sleep-wake cycle of 25-27 hours
• evaluation of circadian rhythms

  • temperature: they can be affected by factors other than light, such as body temperature
  • individual differences: not everyone’s circadian rhythm is the same so it can be hard to generalise findings from studies
  • homeostasis: homeostatic drive for sleep increases throughout the day and tells the body when to go to sleep
• how does the SCN work?

  it sends a signal to the pineal gland, leading to an increase in the production of melatonin at night, helping to induce sleep
• Skene & Arendt (2007)

  studied circadian rhythms in visually impaired people - people without any light perception had abnormal circadian rhythms, showing the importance of exogenous zeitgebers
• ultradian rhythms

  last less than 24 hours and occur more than once throughout the day
• example of an ultradian rhythm

  meal times
• stages of sleep (ultradian)

  • light sleep - brainwave patterns become slower and more rhythmic, individual shows responsiveness to the environment
  • deep sleep - slower delta waves, difficult to wake someone up from this stage
  • REM - dreams occur & the body is paralysed to stop the person acting out their dream
• REM

  rapid eye movement
• NREM

  non-rapid eye movement
• how often does the sleep cycle occur throughout the night?

  every 90 minutes
• evaluation of ultradian rhythms

  • individual differences - people experiences the sleep stages differently, specifically stage 3 and 4
  • lab studies - may be invasive so the person doesn’t sleep how they normally would, affects ecological validity
  • cycles are variable - Randy Gardner stayed awake for 11 days and only recovered 25 % of his lost sleep
• infradian rhythms

  last longer than 24 hours, could be weekly, monthly or yearly
• example of an infradian rhythm

  menstrual cycle
• the menstrual cycle

  regulated by hormones that promote ovulation or stimulate the uterus for fertilisation - ovulation occurs half way through the cycle
• evaluation of infradian rhythms

  • effects - the menstrual cycle can impact behaviour: Penton-Volk et al found that women prefer feminine faces in the least fertile stage, and masculine faces in the most fertile stage
  • exogenous zeitgebers - the menstrual cycle can be governed by external cues such as light
  • individual differences - some women experience shorter cycles than others