exogenous zeitbeigers and endogenous pacemakers

• what are Endogenous pacemakers? 


  • mechanisms within the body that govern the internal biological rythms
• what are endogenous zeitgebers?


  an environmental cue which helps to regulate the bioloigcal clock in an organism 
• light as an exogenous zeitbeiger

  •  The most important exogenous zeitbeiger is Light
  • Receptors in scn detect changes in light levels- info used to synrochise activity of body's organs and glands 
  • Light resets the internal body clock each day maintaining 24 hr cycle
  • Melanopsin is an important protein in retinal cells which is sensitive to natural light and  carries signals to scn to set daily cycle
• • social cues as exogneous zeitbeigers
  • such as meal times and social activities
  • Research found circadian rhythms of travellers adjusted quickly if they went outside and were exposed to social cues of their new time zone- acts as an exogenous zeitgeber
• • endogenous pacemakers
  • The suprachiasmatic nucleus lies in the hypothalamus, it is the main endogenous pacemaker (or master clock). 
  • The SCN receives information about light levels from the optic nerve in the eye (linking from retina)
  • This sets the circadian rhythm so it is in synchronisation with the outside world,
  • It controls other biological rhythms, it links to other areas of the brain responsible for sleep and arousal.
  • sends messages to pineal gland at night to increase the production of melatonin, helping to induce sleep, suppressing it in the day time to wake up
• • Research support from animal studies for the important influence on endogenous pacemakers Morgan bred hamsters so they had circadian rhythms of 20 hours rather than 24 ,scn neurons from these abnormal hamster were transplanted into brains of normal hamsters, which subsequently displayed the same abnormal circadian rhythm, showing the transplanted scn had imposed its pattern onto hamsters,Further evidence in the reverse normal neurons transplanted they cha nged back to 24 hours.  showing the significance of the SCN in the regulation of the sleep wake cycle and the role of endogenous pacemakers. 
  • += issues w animal studies in the case of Morgan's research, in is not certain that transplanting SCN neurons into human brains would have the same affect since human brains are far more sophisticated conclusions drawn must be treated w/ caution
• This is a real life application to the role of exogenous zritbeigers, Butgess found exposure to bright light priori to flying can decrease time needed to adjust to the new time zone on arrival, there were 3 conditions some were exposed to continuous bright light, some intermittent bright light and some a dim light.He found participants exposed to the continuous bright light shifted their circadian rhythm by over 2 hours ove the course of the study, vcompared to just 0.6 for dim light. This suggests an important application that light exposure could be used to reduce jet leg on long haul journeys, which subsequently supports the fact it is a key external factor which has an impact on our circadian rythym

  +t he Burgess et al.study used a total of 26 participants who were healthy young adults from america
• Despite all the research support for the role of endogenous pacemakers and exogenous zeitgebers, the argument could still be considered biologically reductionist. This claim that these contorl bodily rythyms ignores social factors affecting the sleep wake cycle, For example the behaviourist approach would suggest bodily rhythms are influenced by other people and social norms as it wouldn't be socially acceptable to conduct daily routines at night or as a result of operant conditioning eg parents may reward children for going to sleep at their bedtime. It also ignores the fact that humans have the free will to decide to stay awake or sleep longer Whereas this considers a single biological mechanism of an internal biological cycle and fails to consider other viewpoints. ignoring the nurture side of the nature/nurture debate and an interactionist theory may better explain the sleep/wake cycle