a01

• biological rhythm?

  • cyclical changes in the way that biological systems behave
  • evolved due to cyclical changes in the environment
• circadian rhythm?

  repeats every 24 hours
• ultradian rhythm?


  shorter than 24h and occurs multiple times
• infradian rhythm?

  longer than 24h
• circadian rhythm example:

  • sleep wake cycle: strongest drive 2-4am and 1-3pm
  • external zeitgeber: light
  • endogenous pacemaker: SCN & internal clock
• SCN?

  • cluster of nerve cells within the hypothalamus
  • acts as master clock: links to other regions that control sleep and arousal
  • lies just above the optic chiasm and receives information about light directly from it
• SCN 2?

  • continues when our eyes are closed through the eyelids
  • allows our biological clock to adjust to changing patterns of daylight whilst we sleep
  • if our biological clock is running low the morning light automatically adjusts our body clock
• • SCN sends a signal to the pineal gland
  • at night/dark: produces melatonin
  • morning/light:reduces melatonin
• application of melatonin?


  • insomniacs treated with melatonin find it easier to sleep
  • can also be used as treatment for jet-lag
• Exogenous zeitgeber light?

  • receptors in the SCN are sensitive to change in light even when the info is not received by the eyes
  • also influenced bodily processes such as hormone secretion and blood circulation
  • 15ps, light, knee pad= deviation in sleep-wake cycle by up to three hours
• exogenous zeitgeber (social cues)

  • meal times and social activities
  • circadian rhythms begin at about the age of six weeks and by sixteen they are entrained likely due to the schedule of parents
  • jet lag can also be reduced by adapting to local times for eating and sleeping
• Conclusion?

  exogenous zeitgebers and endogenous pacemakers must play a role in our sleep wake cycle