circadian rhythms

• What’s biological rhythm ?

  Repeated patterns of changes in the body that are regulated by an internal clock
• What’s circadian rhythms?

  A biological rhythm that takes about  one day 24 hours to complete a cycle e.g sleep wake cycle 
• How do cyclical change ?

  • They change in the way that biological systems behave 
  • Evolution - the environment has cyclical changes 
• Why are cyclical cycles useful ?

  It optimises physiology and behaviour - day/night cycle and tells our bodies when to sleep,rise,eat - regulating many physiological processes.
• What are some examples of there circadian rhythm ?

  -At 7:30 am melatonin secretation stops and at 21:00 melatonin secretation starts 

  -at 2:00 is our deepest sleep,at 4:00 am is our lowest body temperature and at 19:00 is our highest body temperature 
• What are endogenous pacemakers?

  They are internal body clocks that regulate our body rhythm e.g the suprachiasmatic nucleus 
• What are exogenous zeitgebers ?

  External cues that influence and reset our internal biological clock e.g light 
• What happens when melatonin levels rise ?

  Less light = SCN stimulates the pineal gland to produce more melatonin to help us fall asleep
• What happens when melatonin levels fall ?

  More light = SCN stops pineal gland from producing melatonin to help us feel awake 
• Siffres aim ?

  Siffre aimed to find out what would happen to a person’s circadian rhythms if they were cut off from all zeitgebers, such as light, dark and an awareness of time, and how this would affect their reliance on their endogenous pacemaker to tell them when to eat and sleep.
• Siffres method ?

  The only participant in the experiment was Siffre himself. He spent 179 days and nights in an underground cave. He had no lights, clocks or radios to give him any indication of what time it was and so his only influence was his internal body clock, which had a ‘free run’ to do what felt natural.

  His only link to the outside world was a telephone where he could keep in touch and was also monitored by video camera and by wires attached to his body that monitored how he was functioning.
• Siffres result ?

  • At first, Siffre’s sleep-wake patterns were very erratic
  • After a while, they settled into a 25-hour pattern rather than 24 hours, which is the time a human considers to be a full day and therefore how long a sleep-wake cycle should last
• Siffres conclusions ?

  Siffre concluded that humans do have a natural sleep-wake cycle, but without the influence of external zeitgebers it naturally settles into a 25-hour pattern, so an hour longer than what people would experience normally.
• What’s some evaluations for siffres research ?

  • :( research tends to include small sample or individuals siffre - didn’t get the same results when younger 
  • :( siffres results was supported by a study from Folkard
  • :) real world application - chronotherapeutics - study of how timing affects drug treatment