Circadian rhythms

• Circadian Rhythms


  A biological rhythm that takes about 24 hours to complete a cycle
• Give an example of a circadian rhythm

  Sleep wake cycle
• Siffre's cave study

  • Spent several extended periods underground to study his biological rhythm
  • Deprived of natural light and sound
  • He once stayed there for 2 months thinking it had only been a month
  • He did it again for 6 months
  • His biological rhythm was around 25 hours and he had schedule of waking up and going to sleep
• Research on Circadian Rhythms

  • PPs spent 4 weeks in a WWII bunker deprived of natural light
  • All PPs displayed a cycle between 24 and 25 hours apart from one PP who had a cycle of 29 hours
• What did Siffre's cave study find?

  1. We have an internal biological clock that controls our circadian rhythm
  2. Our sleep wake cycle may be nearer to 25 hours
  3. We need exogenous zeitgebers to help regulate our sleep wake cycle
• AO3 Circadian Rhythms: Shift Work

  • Provides understanding of the consequences of a disrupted sleep wake cycle
  • Night workers experiences reduced concentration around 6 in the morning so more accidents happen
  • There is a relationship between shift work and poor health- 3 times more likely to get heart disease
  • Can help worker productivity
• AO3 Circadian Rhythm: Medical Treatment

  • Circadian rhythms coordinate a number of the body's basic processes such as heart rate and digestion
  • Medicine has been created to correspond to a person's biological rhythm
  • Aspirin treats heart attacks and better taken at night
  • Can help the effectiveness of drug treatment
• AO3 Circadian Rhythm: Individual Differences

  • Generalisations are difficult to make
  • The research studies had small samples and sleep wake cycles vary for different people
  • It is difficult to use research data based on other people
• AO3 Circadian Rhythm: Research Support

  •  Research has been conducted to investigate circadian rhythms and the effect of external cues like light on this system
  • Siffre found that the absence of external cues significantly altered his circadian rhythm
  • When he returned from the cave with no clocks or light he thought time had gone quicker
  • His sleep wake cycle was increased by the lack of external cues making him believe one day was longer than it was
  • Provides support for a free running circadian rhythm
• AO1 Circadian Rhythm

  • Sleep wake cycle is an example which dictates when humans should be asleep and awake
  • Light involved the primary input to the system acting as an external cue for sleeping or waking
  • Light is first detected by the eye which send signals of levels of brightness to the SCN
  • This is an endogenous pacemaker which helps us determine when to sleep