Biological Rhythms

• circadian rhythm


  24 hours
• infradian rhythm


  longer than 24 hours
• ultradian rhythm


  less than 24 hours
• what is an example of a circadian rhythm?

  sleep wake cycle
• what is an example of an infradian rhythm?

  menstrual cycle
• what is an example of an ultradian rhythm?

  stages of sleep
• how might stages of sleep be measured?

  eye movements
• what might lead to desynchronisation of circadian rhythms?

  shift work and jet lag
• explain the process of waking up in terms of a circadian rhythm

  high light intensity --> light receptors in eye --> suprachiasmatic nucleus --> pineal gland --> inhibits melatonin --> awake
• what research supports circadian rhythms?

  siffre - case study - spent two months in a cave deprived of light and sound - sleep wake cycle remained the same
• what is a limitation of research into circadian rhythms?

  case study cannot be generalised beyond individual experience
• what research is there on infradian rhythms?

  mclintock - found menstrual cycles can be synchronised through pheromenes
• what is a strenght of research into infradian rhythms?

  evolutionary benefit - all ancestors give birth around the same time - children can be cared for collectively - greater chance of survival
• what research is there on ultradian rhythms?

  kleitman et al - used EEGs and found that dreaming occurs during the REM stage of sleep
• what is a strength of research into ultradian rhythms?

  EEG is a reliable measure as is standardised and objective
• what is a limitation of research into ultradian rhythms?

  lacks temporal validity - research conducted in 1950s to cannot be generalised to current time
• endogeneous pacemakers


  internal mechanisms which determine the biological rhythms of the body
• what is an example of an endogenous pacemaker?

  suprachiasmatic nucleus
• exogenous zeitgebers


  any factor which acts as an external cue
• what is an example of an exogenous zeitgeber?

  light