circadian rhythms

• biological rhythms

  distinct pattens of changes in body activities that conform to cyclical time periods. Influenced by internal body clocks as well as external changes to the environment
• Circadian rhythms

  biological rhythms subject to a 24-hour cycle, which regulates a number of body processes such as sleep/wake cycle and changes in core body temperature
• biological rhythms are governed by:

  • internal biological clocks - endogenous pacemakers
  • external changes in the environment - exogenous zeitgebers
• biological rhythms:

  • ultradian rhythm
  • circadian rhythms
  • infradian rhythm
• two examples of circadian rhythms:

  1. sleep/wake cycle
  2. core body temperature
• the sleep/wake cycle - exogenous zeitgebers

  • drowsy at night-time and alert during day -> effect of daylight (exogenous zeitgeber) on our sleep/wake cycle
• the sleep/wake cycle - endogenous pacemakers

  suprachiasmatic nucleus (SCN) - biological clock above the optic chiasm

  optic chiasm - provides info from the eye about light

  exogenous zeitgebers resets SCN
• Siffre's cave study:

  • spent several extended periods underground to study the effects on his own biological rhythms
  • deprived of exposure to natural light and sound but with access to food and drink
  • Siffre resurfaced in mid-september thinking it was august after two months in the caves
  • did it again a month later for 6 months
  • his 'free-running' biological rhythm settled down to once that was just beyond the usual 24 hours though he did continue to fall asleep and wake up on a regular schedule

  
• research - circadian rhythms

  • aschoff and wever - convinced group of ppts to spend 4 weeks in WW2 bunker deprived of natural light all but one of the ppts displayed circadian rhythm between 24-25 hours
• research conclusions - circadian rhythms (siffre + aschoff and wever

  • suggest that the natural sleep/wake cycle may be slightly longer than 24 hours but it is entrained by exogenous zeitgebers
• circadian rhythms

  • we should not overestimate the influence of exogenous zeitgebers on our internal biological clock
  • FOLKARD - studied group of 12 people who lived in a dark cave for three weeks went to bed at 11:43 and rising at 7:45
  • researchers gradually sped up the clock (day last only 22 hours)
  • only one ppts adjusted
  • existence of free-running circadian rhythm cannot be easily overridden by exogenous zeitgebers
• circadian rhythms - AO3 - shift work

  • provides understanding of the adverse consequences that occur when they are disrupted
  • night workers engaged in shift work - period of reduced concentration around 6 in the morning meaning more mistakes
  • relationship between shift work and poor health - 3x more likely to develop heart disease than people who work typical work patterns
  • real-world economic implications
• circadian rhythms - AO3 - improves medical treatment

  • circadian rhythms co-ordinate a number of the body's basic processes such as heart rate, digestion and hormone levels
  • these rise and fall during the course of a day
  • led to cronotherapeutics
  • aspirin more effective at night as heart attacks are most likely to occur in the morning - redices blood platelet activity
• circadian rhythms - AO3 - individual differences

  • generalisations are difficult to make
  • supporting studies are based on very small samples on ppts
  • sleep/wake cycles vary from person to person
  • Duffy - some people prefer going to bed early and rising early or the opposite
  • difficult to use the research data