Endogenous and Exogenous Flashcards
What are EnDOGENOUS PACEMAKERS?
biological clocks that set our free running internal rhythm. Most organisms have an internal clock that matches the time passage of the 24 hour day
What are endogenous pacemakers and exogenous zeitgebers relationship with each other thought to be?
Thought to interact in the control and fine-tuning of our bio rhythms
What is the main pacemaker?
Cluster of nerve cells known as the suprachiasmatic nucleus (SCN)
How does the SCN work?
- Information obtained via optic nerves about light
- Sends signals to pineal gland
- Regulates production of melatonin, which in turn induces sleep and inhibits mechanisms that promote wakefulness
What happens to melatonin production in the presence of light?
Inhibits the production, with the SCN indirectly involved in this process and causing an individual to feel more alert
Evidence for the importance of the SCN has been found in a study by Morgan…
Mutant hamsters bred with circadian rhythms of 20 hours rather than 24. SCN of mutant hamsters transplanted into normal hamsters, where normal hamsters developed rhythm
What does Morgans mutant hamster study demonstrate?
The key role the SCN plays as the main endogenous pacemaker
How does the SCN support an evolutionary approach?
- May have adaptive advantage
- Allows animal to anticipate daily environmental events
What did Decoursey find regarding adaptive advantages of the SCN?
- SCN destroyed in some chipmunks
- Far more active at night that non-modified, so more likely to be harmed by nocturnal predators
Why has Decourseys/SCN research been criticised?
- Involvement of non-human studies
- Different anatomy, so findings may be lacking in external validity and cannot be generalised
- Ethical concerns
What can’t endogenous pacemakers function accurately in the absence of?
Exogenous zeitgebers - in it’s absence, EP’s can become desynchronised
What did Folkard et al find regarding Kate Aldcroft
- Short amount of time in a cave, so was free from EZ’s
- After 25 days, her temp rhythm was 24 hour cycle but her sleep rhythm was 30 hours
What does Kate Aldrofts results show?
- Existence of separate EPs aside from the SCN
- Can become desynchronised without EZ’s
What is the role of exogenous zeitgebers?
Keeps the free running biological rhythm regulated effectively
What are some examples of EZ’s?
- Social cues like meal times and other social conventions entrain our bio rhythms
- Dominant zeitgeber is light
- Temperature e.g. deciduous trees
What is the effect of bright light as a dominant EZ?
Inhibits melatonin, meaning that daylight ‘sets’ the biological clock at the beginning of each day. Hold the potential to shift the internal clock forwards or backwards
What did Campbell and Murphy do in their study of bright light as a EZ?
- Light shone on back of PPS knees
- Shifted circadian rhythms
Why might the SCN not be the main endogenous pacemaker?
Other oscillators must exist that compensate by keeping bio clock in tune with outside world
There is conflicting evidence to suggest that artificial light is the dominant zeitgeber.
- Siffre and Aschoff assumed that it would not be efficient enough
- Boivin: rhythms can be entrained by dim lighting
What do Boivins findings pose the question of?
Negative consequences for individuals if it does in fact reset the bio-clock
What negative consequences might artificial light have?
Stevens - artificial light - disrupts melatonin production leading to higher incidences of breast cancer in well lit areas
What is a positive application of Stevens’ research?
-Could be used to influence shift work patterns and thus aid workers in avoiding devastating health complications
What is the overall point?
Necessary to emphasise - intertwined sysyem that are not separately existing
