Endogeneous pacemakers and Exogeneous zeitgabers

• Exogeneous zeitgeber

  External 'time-giving' factors e.g. light, clocks
• Endogenous pacemaker

  Internal biological rhythms that control sleep
• Endogenous pacemaker - The SCN and how it works

  The suprachiasmatic nucleus is a bundle of nerves located in the hypothalamus in each hemisphere of the brain. It is one of the primary endogenous pacemakers in mammals and is influential in maintaining biological rhythms such as the sleep/wake cycle

  Nerve fibers connected to the eyes cross in an area called the optic chiasm on their way to the processing area of the cerebal cortex. The SCN lies just above the optic chiasm. The SCN revieves information about synchronisation directly from the optic chiasm. This continues even when our eyes are shut. This enables the biological rhythms to adjust to changing patterns of daylight even whilst we are asleep
• De Coursey et al (2000)

  Collected 30 Chipmunks and destroyed their SCN, returned them to their natural habitat and observed for 80 days, once released back to the wild their sleep-wake cycle had disappeared and a significant proportion of them had been killed by predators
• Ralph et al (1990)

  Bred hamsters whom had a 20 hour sleep-wake cycle. Transported foetal tissue form these ino natural hamsters and these began to run on a 20 hour cycle This shows that biology has a huge impact on the sleep- wake cycle
• What's the pineal and melatonin role in the sleep wake cycle

  The SCN passes the information on day length and light that it receives to the pineal gland. The pineal gland is a pea-like structure in the brain just beyond the hypothalamus. During the night, the pineal gland increases production of melatonin. This is the chemical that induces sleep and inhibited during periods of wakefulness. Melatonin has been suggested as a casual factor in seasonal affective disorder
• Exogenous zeitgebers

  Exogeneous zeitgebers are external factors in the environment that sync with our biological clocks through a process known as entrainment. Without external cues the free running biological clock controls the sleep-wake cycle. This shows that the sleep/wake cycle is determined by a mixture of endogenous and exogenous factors
• Light

  This is a key zeitgeber in humans . It can reset the body's main endogenous pacemaker, the SCN, so plays a role in the maintenance of the sleep/wake cycle. Light also has an indirect influence on key processes in the body that control such functions as hormone secretion and blood circulation
• Exogenous zeitgeber - Social cues

  Babies are rarely in the same sleep-wake cycle as the rest of the family. In human infants the sleep wake cycle is apparently underdeveloped. Circadian rhythms begin around 6 weeks of age and by 16 weeks most babies are entrained. The schedules imposed by parents will be a key to influence sleep-wake cycles including mealtimes and bed times

  Research suggests that adapting to local times for eating and sleeping is an effective way of entraining biological rhythms and beating jetlag when travelling long distance
• Cambell and Murphy (1998)

  Woke 15 participants at various points and a light pad was shon on the back of their knees. This resulted in a deviation in participants normal sleep- wake cycle
• Weakness of pacemakers and zeitgabers

  ❌ The research used here tries to isolate endogenous pacemakers from exogeneous zeitgebers which provides greater clarity in research but this doesn't reflect real-life as the two would never operate in isolation. It is also impossible to test this in experimental conditions , for example even Siffre used artificial light in his experiment which means zeitgebers may have played a role
• Weakness of endogenous pacemakers and exogenous zeitgebers

  ❌ Much of this research which supports the role f endogenous pacemakers in animal research. Therefore we cannot assume that human behaviour would be affected in the same way. Equally the ethic of these studies could be questioned. Human research needs to be conducted to allow those conclusions to be made
• Weakness of endogenous pacemakers and exogenous zeitgebers

  ❌ Research has suggests that there may be as many as 100 separate pacemakers involved in various biological processes. These pacemakers may run irrespective of the SCN. For example Damiola et al (2000) demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours without effecting the SCN
• Weakness of endogenous pacemakers and exogeneous zeitgebers

  ❌ There is a a variation in the reports of people living in extreme environments of the role of zeitgebers on the sleep wake cycle. for example Inuit eskimos who live in the artic circle report having the same sleep/wake cycle year round, despite spending six months in almost total darkness. This suggests that zeitgebers might not affect everyone in the same way
• Advantages of endogenous pacemakers and exogeneous zeitgeber research

  If we understand the role of zeitgebers play in biological rhythms than we can use the, to help in treatment/intervention. For example we could use zeitgebers in helping those who do shift work adjust to night time shifts. This could be positive to the economy as shift workers become more productive and less likely to take absence
• Advantages of endogenous pacemakers and exogeneous zeitgeber research

  ✔️ Miles et AL (1997) provided evidence of a blind man who had a sleep-wake cycle of 24.9 hours. Despite being exposed to social cues his rhythm did not adjust and therefore he had significant problems adjusting to waking and sleeping. This supports the idea that light is the most important zeitgeber for the sleep wake cycle