Biological Rhythms

• What does Infradian mean ?

  • Longer than a day
• What are the three types of Biological Rhythms ?

  1.) Infradian Rhythms

  2.) Circadian Rhythms

  3.) Ultradian Rhythms
• What does Infradian Rhythms mean ?

  • Longer than a day
• What does Circadian Rhythms mean ?

  • About a day
• What does Ultradian Rhythms mean ?

  • Shorter than a day
• What is an example of Infradian Rhythms ?

  • Menstruation
• What is an example of Circadian Rhythms ?

  • The sleep-wake cycle
• What is an example of Ultradian Rhythms ?

  • Stages of sleep
• How are biological rhythms controlled ?

  • They are controlled by internal mechanisms called endogenous pace makers in combination with external mechanisms called exogenous Zeitgebers
• What is the sleep-wake cycle ?

  • It is a circadian rhythm
• What does the sleep-wake cycle do ?

  • It determines when we sleep and wake during the 24 hour day
• What are the two mechanisms that control the sleep-wake cycle ?

  1.) Endogenous pacemakers

  2.) Exogenous Zeitgebers
• What are Endogenous pacemakers ?

  • Internal biological mechanisms that suddenly produces timed rhythmic activity
• What are exogenous zeitgebers ?

  • External factors that 'tune' the cycle into environmental factors
• What is the name of the main endogenous pacemaker for the sleep-wake cycle ?

  • Suprachiasmatic Nucleus
• Where is the suprachiasmatic nucleus located ?

  • It is a tiny region of the hypothalamus
• What does the suprachiasmatic nucleus do ?

  • It acts as a biological clock whose production of proteins rises and falls over a 24 hour cycle
  • This rhythmic activity is free running and genetically determined
• What is the main type of endogenous pacemaker ?

  • The main endogenous pacemaker for the sleep wake cycle is the Suprachiasmatic Nucleus, that acts as a biological clock
• What is the main type of Exogenous Zeitgebers ?

  • The main Exogenous Zeitgeber is light
  • low levels of light are detected by melanopsin (protein) in the retina that passes the information to the Suprachiasmatic Nucleus (SCN) via the optic nerve
  • The SCN instructs the Pineal Gland to convert serotonin release into melatonin
• What are two other examples of exogenous Zeitgebers ?

  1.) Social Activities

  2.) Meal times
• What is a research support for the role of Endogenous pacemakers and Exogenous Zeitgebers ?

  • Morgan (1955) bred hamsters so that they had abnormal Circadian Rhythm of 20 hours and not 24 hours
  • He then transplanted the neurons of the abnormal hamsters to normal ones which changed the normal hamsters circadian rhythm to 20 hours
  • Then he transplanted normal hamsters suprachiasmatic nucleus to abnormal hamsters and it changed to 24 hours
  • This shows the importance of the SCN
• What is a research support for Melanopsin ?

  • Skene et al (2007)
  • They estimated that the majority of blind people who still have some light perception have normally trained their Circadian rhythm
  • Suggesting that retinal pathways that contain Melanopsin to the SCN is still intact
• What is Melanopsin ?

  • It is a protein in the retina that passes information to the suprachaismatic nucleus
• What is a research support for the Circadian Rhythm ?

  • Siffre was a cave explorer who spent several weeks or months underground away from natural light
  • He found that he maintained a 'free running' Circadian Rhythm that lasted a little longer than 24 hours
  • This shows that biological rhythms can persist without external cues (exogenous zeitgebers)
• What is real world application for the sleep-wake cycle ?

  • International air travel disrupts biological rhythms especially when traveling from west (US) to east (UK)
  • To decrease the effect of jet lag, light therapy or melatonin could be used
• What is the main type of exogenous zeitgeber ?

  • light
• Who did the research support for the role of Endogenous pacemakers and Exogenous Zeitgebers ?

  • Morgan (1955)
• What did Morgan (1955) use to investigate the role of Endogenous pacemakers and Exogenous Zeitgebers ?

  • Hamsters
• What did Morgan breed hamsters to have ?

  • Abnormal circadian rhythms of 20 hours and not 24 hours
• Who did research support for Melanopsin ?


  Skene et al (2007)
• What did Skene et al estimate that the majority of blind people who still have some light perception have ?

  • They have normally trained their Circadian Rhythm
• What did Skene et al (2007) research support for Melanopsin suggest ?

  • It suggests that retinal pathways that contain Melanopsin to the SCN is still intact
• Who did Research support for the Circadian Rhythm ?

  • Siffre
• What did Siffre find that he managed to maintain ?

  • A 'free running' Circadian Rhythm that lasted a little longer than 24 hour
• What did Siffre's 'free running' Circadian Rhythm show ?

  • It shows that biological rhythms can persist without external cues (exogenous zeitgebers)
• Name what a real world application for the sleep-wake cycle is ?

  • International air travel
• What does international air travel disrupt ?

  • Biological Rhythms
• What are two ways to deal with jet lag ?

  1.) Light therapy

  2.) Melatonin