endogenous pacemakers and exogenous Zeitgebers Flashcards
what is an endogenous pacemaker?
our internal body clocks that regulate biological rhythms (often through the release of hormones)
what is an exogenous zeitgeber?
external changes to the environment that helps to regulate our internal body clock (such as changes in daylight)
what is the suprachiasmatic nucleus (SCN)?
is located in the hypothalamus and it is the main endogenous pacemaker, it is our master clock.
how does the SCN work?
The SCN also receives information about light levels from the optic nerve, which sets the circadian rhythm so that it is in synchronisation with the outside world. Melanopsin is a protein in the eye which is sensitive to light and carries the signal to the SCN. The SCN sends signals to the pineal gland which leads to an increase in the production of melatonin at night, helping to induce sleep.
what do exogenous zeitgebers do to our biological clock?
Exogenous zeitgebers entrain our biological clock to a 24 hour cycle.
what are the social factors that help entrain our biological clock?
They can include social cues such as meal times and social activities. For example, some social cues such as reading or watching specific tv shows to trigger the bedtime process.
how does light help to entrain our biological clock?
However the most important zeitgeber is light, this is responsible for resetting the body clock each day, keeping it on a 24-hour cycle. By reducing light, this enables the body to increase the production of melatonin meaning we start to become more tired.
AO3: how is ‘support for the role of the SCN’ a strength to endogenous pacemakers and exogenous zeitgebers?
one strength to the role of endogenous pacemakers and exogenous zeitgebers is that there is supporting evidence for role of the SCN. DeCoursey removed the SCN from 30 chipmunks and returned them to their natural habitats where they were observed for 80 days. They found that a significant amount of the chipmunks had died when they had no SCN compared to the control group with normal functioning SCNs. This suggests that endogenous pacemakers have an important role when giving cues to the body for when it requires basic needs such as sleep, food or to drink. This helps to explain why the chipmunks with no SCN died as they were unable to feel when they needed to sleep meaning they may have died from overexhaution, or as they no longer have a biological sleep/wake cycle, they may have gone outside at night when there were predators. This therefore supports the idea that endogenous pacemakers have a higher influence on our biological rhythms than endogenous zeitgebers.
However, one issue with this research is that it has ethical concerns. This is because it involves removing parts of the chipmunks brain and then seeing how long it took for them to die in the wild without their instincts, exposing them to deadly risks.
AO3: how is ‘support for a strong running SCN’ a strength to endogenous pacemakers and exogenous zeitgebers?
one strength to the role of endogenous pacemakers and exogenous zeitgebers is that there is supporting evidence for a strong running SCN. Siffre conducted a cave study where he deprived himself of natural light and sound but had access to drinks and food. He found that his free running biological rhythm settled down to one slightly longer than the normal 24 hours with the aid of social cues. This supports the role of endogenous pacemakers as his body settled into the 24 hour cycle, suggesting that our internal rhythms do have an important effect on our biological rhythms. However, this also provides evidence for the role of exogenous zeitgebers as his biological rhythm did move slightly compared to a normal rhythm. This suggests that we do need external cues such as meal times and sunset to keep our biological rhythm to exactly 24 hours. Therefore, this supports the idea that we need both exogenous zeitgebers and endogenous pacemakers to keep our biological rhythms controlled at 24 hours.
However, this research lacks ecological validity as the study was done in a cave, meaning we have to take care when generalising the findings to other more daily settings as behaviours in a cave are different to behaviours in every day life.
AO3: how is ‘research lacks generalisability’ a limitation to endogenous pacemakers and exogenous zeitgebers?
one limitation to endogenous pacemakers and exogenous zeitgebers is that the research into it lacks generalisability. This is because when using animals in research, we have to be careful when applying the concluded findings as the human brain and behaviour is much more complex. Humans are also much more self aware compared to chipmunks, meaning that the findings from the chipmunk study have to be used with caution as they are unrepresentative of human behaviour. We also have to be careful when generalising the findings of Siffre’s study due to it being a case study. This is because his findings are based upon a single person, which means that it is unrepresentative of the wider population. This therefore suggests that we have to be careful when using the findings from particular studies when looking into endogenous pacemakers and exogenous zeitgebers.
AO3: how is ‘real life application’ a strength to endogenous pacemakers and exogenous zeitgebers?
one strength to research into endogenous pacemakers and exogenous zeitgebers is that the research can be applied to real life. Hood found that insomnia can be improved if elderly people were more active and had greater exposure to natural light. This supports the idea that exogenous zeitgebers are important in helping to regulate and normalise our sleep wake cycle and biological rhythms. By understanding the cues that help our biological rhythms, we can help new parents when trying to get their babies into a regular cycle. We can do this by giving them a daily routine such as set meal times during the day, exposure to natural sunlight during the day and blackout blinds during the night and doing things before bed such as reading or having a bath. These external cues allow the children to develop and maintain a regular 24 hour rhythm. Therefore, by understanding the role of endogenous pacemakers and exogenous zeitgebers, we can help educate parents on the importance of the external cues in maintaining our biological rhythms.
