The role of endogenous and exogenous in biological rythems

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  • The role of endogenous pacemakers and exogenous zeitgebers in biological rythems
    • an endogenous pacemaker is an internal regulator of our 'body clock'- the main one being the suprachiasmatic nucleus (SCN) which takes information from the optic nerve and sends it to the pineal gland which regulates melatonin accordingly
    • an exogenous zeitgeber is an external cue in the environment that helps to regulate biological rythems
    • A circadian rythem occurs once every 24 hours- for example the sleep wake cycle- research has been carried out to see if there is mainly an internal or external influence on regulating these rythems
      • role of endogenous pacemakers in circadian rythems
        • Stephan and Zucker- found that damaging a rats SCN resulted in elimination of regular circadian drinking activity
          • however this may have been a result of the traumatic procedure- also animal research- not humans
          • Zucker Rusak- found similar results in hamsters when the circannual rythem of testosterone secretion was disrupted by SCN damage
            • also similar to Ralph et al- who found conditioned a rats SCN to the rythem of 20.5 hours- then removed it and put it into another hamster which then adopted the donor hamsters shortened rythem
      • the role of exogenous zeitgebers on circadian rythems
        • Siffre- found that exogenous zeigebers influence our circadian rythems when he spend 6 months in a cave with one way communication to his team to tell them when he wanted food or the lights switching on
          • his SCN was 'freerunning' which resulted in him losing 28 days when he got out, and his sleep-wake cycle extending to 25-27 hours
            • supported by Aschoff and Webber who found that student's sleep-wake cycle extended to 25-27 hours when they lived in underground bunkers
    • an infradian rythem occurs more than every 24 hours-  for example hibernation or the menstrual cycle
      • the role of endogenous pacemakers on infradian rythems
        • Alexander and Brookes- the skin shedding of snakes kept in 12hour light/dark at 25 degrees for 7 years- still remained the same
        • Reiberg- women living in a ave together whose menstrual cycles shortened- but was still maintained in the absence of external cues
      • the role of exogenous zeitbgebers on infradian rythems
        • Goss- deer antler shedding associated with longer days towards summer
        • Mckintosh- women living together in uni halls started to synchronize their menstrual cycles
          • Supported by Weller and Weller who found that women who live togerter all of the time, e.g. lesbians or mother/daughter/sister or friends also synchronized theri menstrual cycles
            • this can be explained and supported by a controversial study by Russell et al- who swabbed a females armpit to extract her pheramones and placed it on another womans upper lip- they found that the woman took on the menstrual cycle of the donor
    • mainly animal research used so unethical and invalid with low ecological validity
    • not much research into males- gender bias
    • ethnocentric to western culture
    • determinsistic


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