biological rhythms

• A biological rhythm is a pattern of change in the body that occurs in cycles and repeats.
• Ultradian rhythms:

  • stages of sleep
  • 5 stages of sleep per cycle
  • each cycle lasts about 90 minutes
  • stage 1 and 2 is light sleep
  • stage 3 and 4 is deep sleep
  • stage 5 and 6 is REM sleep
  • Rapid eye movement is when dreaming occurs and memories are formed in this stage
• Evaluation of ultradian rhythms:

  🙂 evidence to support - Dement and Kleitman

  🙂 practical applications - sleep disorders
• Infradian rhythms

  • menstrual cycle
  • change in hormone levels
  • cycle takes 28 days to complete
  • rising levels of the hormone oestrogen (ovulation)
  • after ovulation the hormone progesterone helps the womb lining grow thicker
• Evaluation of infradian rhythms

  ☹️ evidence to contradict - Yank and Schank

  ☹️ methodological problems - extraneous variables
• Circadian rhythms

  • the sleep/wake cycle
  • lasts 24 hours
  • affected by both internal and external factors
  • internal factors are our endogenous pacemakers
  • external factors are our exogenous zeitgebers
• The suprachiasmatic nucleus (SCN)

  • small bundle of nerve cells found in the hypothalamus
  • receives information about light
  • SCN is affected by external cues (light and dark)
  • however it has its own internal activity rhythm
• 1. the SCN passes information about light to the pineal gland
  2. during the night the pineal gland converts serotonin into melatonin
  3. melatonin makes you feel less alert and sleepy
• DeCoursey’s research

  • destroyed the SCN connections in the brain of 30 chipmunks
  • they were returned to their natural habitat and observed for 80 days
  • the regular sleep/wake cycle of the chipmunks disappeared
  • many were killed by predators as they were more vulnerable
  • shows importance of SCN in establishing and maintaining the circadian sleep/wake cycle
• The effect of exogenous zeitgebers on the sleep wake cycle

  • artificial light
  • social cues
  • the SCN naturally runs a rhythm of about 25 hours
  • influence of exogenous zeitgebers regulates it to about 24 hours
• Circadian rhythms evaluation

  🙂 evidence to support endogenous pacemakers - Siffre’s cave

  🙂 evidence to support endogenous pacemakers - Ralph’s hamsters

  🙂 Evidence to support exogenous zeitgebers - Campbell and Murphy’s knees

  🙂 Practical applications - supporting shift workers