EZs and EPs

• Exogenous Zeitgebers (EZs) - an environmental cue, such as light or social cues that help to regulate the biological clock in an organism
• Endogenous pacemakers (EPs) - mechanisms within the body that govern the internal bodily rhythms
• EZs - things that happen outside (social cues)

  EPs - internal biological clock (SCN)
• SCN is the master circadian rhythm pacemaker found in the hypothalamus.

  • it receives light info from the eye
• The SCN sends signals to other parts of the brain which control sleep/wake cycles.
• Research support - Role of SCN

  Morgan - mutant hamsters study

  • bred hamsters with a 20 hour rhythm and transplanted the SCN to 'normal' hamsters who then displayed the 20 hour cycle

  shows the vital role the SCN plays in shaping cycles
• Role of EZs - Aldcroft

  • spent 25 days in a lab with not light (EZs) and found her sleep/wake cycle slipped to 30 hours

  shows the effects of EZs
• Real world application - Light exposure to avoid jet lag

  Burgess et al

  • exposure to bright light prior to an east-west flight decreased the time needed to readjust to local time by up to 2 hours
• Circadian rhythm - pattern of behaviour that occurs roughly every 24 hours (e.g. sleep-wake cycle)
• The cave study - Siffre

  Evidence for the 'free-running' circadian rhythm

  • stayed underground for extended periods of time with the absence of all EZs
  • found changes in his circadian rhythm