Circadian rhythm

• Biological rhythm def


  Distinct pattern of changes in body activity/processes in response to cyclical changes within the environment/in response to cyclical time period
• What are the 2 things biological rhythms are influenced by


  -Exogenous zietgebers

  -Endogenous pacemakers
• What is exogenous zeitgebers

  External events responsible for setting biological rhythms
• What are the 4 types of biological rhythm

  -Circadian

  -Circannual

  -Ultradian

  -Infradian
• What is circadian rhythm

  Biological cycles that occrs every 24 hrs eg sleep/wake cycle
• What is circannual rhythm

  Takes about 1 yr to complete eg migration of birds, hibernation of animals
• What is ultradian rhythm


  Biological cycles that occur more than 1x a day eg diff stages of sleep
• What is infradian rhythm


  Biological cycles that last longer than 24hrs eg womens menstrual cycle
• How is body temp an example of circadian rhythm

  -Lowest at 4:30am

  -Highest at 6pm daily
• Why is body temperature important?

  -Sleep occurs when core temp starts to drop

  -Body temp rises at end of sleep cycle, promoting alertness in morning

  -Warmer=better cognitive performance
• How is the sleep/wake cycle a circadian rhythm

  We feel drowsy at night & alert in day
• What exogenous zeitgeber is involved in sleep/wake cycle

  Sunlight
• What did Siffre do

  1)Spent time underground (deprived of natural light &sound) to study bio rhythm

  2) Spent 2 months in cave in Southern Alps

  3) Came out of care in Sep 1962, thinking it was August

  4)A decade later, spent 6 months in Texan cave

  5)His "free running" biological rhythm settle down to 25hr cycle but fell sleep & awake at regular times
• What did Aschoff and Wever do?

  1) Ppt spent 4 weeks in WW11 bunker, deprived of natural light

  2)All but one displayed a circadian rhythm 24-25hr (other one had 29hr)
• What does Siffre and Aschoff & Wevers study suggest

  Natural sleep cycle may be slightly longer than 24hrs but exogenous zietgeber still influences it (eg daylight hrs & meal times)
• Folkard


  -!2 ppl in dark cave for 3 weeks

  -Went to sleep at 11:45pm and awoke at 7:45

  -Researchers gradually sped up clock so apparent 24hr day was 22hr

  -Not one could comfortably adjust
• Evaluation... ...
• Strengths of circadian rhythm studies

  +Practical application to shift work

  +Practical application to drug treatment
• How is practical application to shift work a strength

  -Desynchronisation

  -Biovin- night workers have reduced concentration at 6am (when accident most likely to occur)

  -Knutsson- shift workers more likely to develop heart disease (due to stress trying to adjust to diff sleep/wake cycle & poor quality sleep during day?)
• What is desynchronization?


  Disruption of circadian rhythm
• How is practical application to drug treatment a strength

  -Circadian rhythm coordinates some of bodys processes (eg bpm, blood pressure, digestion).

  -This effects how well medication is absorbed and distributed in body

  -eg aspirin most effective last thing in the day.

  -It reduces platelet activities & risk of heart attacks that occur early in morning
• What are the limitations of circadian rhythm studies

  -Case studies & small samples

  -Poor control in research studies

  -Indv differences
• How is small sample a weakness

  -Siffre used himself as a subject
• How is poor control in research studies a weakness

  -Ppt deprived of natural light but still had artificial light

  -Eg Siffre turned on torch when he woke up

  -Researchers assumed light had no affect on bio clock but wrong

  -Czeisler could change ppt circadian rhythm from 22-28hr
• How are individual differences a weakness

  -Indv sleep/wake cycles vary

  -Czeisler found cycles can vary between 13-65hr

  -Duffy found some ppl prefer to go to sleep & wake up earlier (morning lark) or vice versa (night owl)

  -Also age differences
• How does circadian rhythm research support shirting school day

  -Suggest starting schools later will fit typical chrono type

  -Hormonal shifts in teens make them sleepier at start of day

  -Proved that academic & behavioural performance increase when school starts late

  -BUT may be problem for teachers & parents & Amy limit extraurriculars