Endogenous Pacemakers and Exogenous Zeitgebers

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  • Endogenous Pacemakers
    • Endogenous pacemakers are internal factors that regulate the sleep-wake cycle. Some aspects of our biological rhythms are set by genetic structures within the body.
    • In 1995 Morgan conducted a study where he bred hamsters to a have a circadian rhythm of 20 hours. He then implanted the neurons to a normal hamster which in turn changed it's body clock to be 20 hours
    • This supports endogenous pacemakers and  and shows that abnormal SCN's can lead to abnormal circadian rhythms
    • In some situations the body clock can become out of sync. In 1996 Folkard studied a uni student who spent 25 days in a controlled environment and had no access to natural light.
    • This showed the circadian rhythm had changed to 30 hours and upto 16 hrs sleep
  • Exogenous Zeitgebers
    • Exogenous zeitgebers are external factors that act as a prompt, which may trigger a biological rhythm. Light is the most important zeitgeber.
    • Receptors in the SCN are sensitive to light changes and use this info to synchronise the body clock.
    • Melanopsin is found in protein in the cells in the eye and carry signals to the SCN to set the body clock
    • There are also social cues e.g. mealtimes and social activities that may act as zeitgebers. These could compensate for the lack of natural light.
    • Some blind people are able to entrain their circadian rhythm in response to light. Where as people without light perception have abnormal circadian rhythms.
    • Burgess in 2003 found that exposure to bright light prior to an east west flight decreased time needed to adjust to local time on arrival. They were subjected to light for one hour over 3 days.
    • This changed their circadian rhythm by 2.1 hours. Which made them closer to local time. This hows that light plays an important part in maintaining circadian rhythms.
    • Vetter in 2011 investigated the impact of artificial light. P's were shown 'warm' and 'blue' light which went back by 42 mins over 5 weeks.
    • The 'warm' subjects circadian rhythms changed by 42 mins and the 'blue' p's rhythms did not change.

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