Endogenous Pacemakers, Exogenous Zeitgebers Essay Plan

2. Describe in detail exogenous zeitgebers- resetting the biological clock (entrainment). Light resets the SCN, also resets other oscillators located throughout the body as the protein CRY, part of the protein clock is light sensitive. Darlington- morning two proteins bind together CLOCK and CYCLE, once joined, CLK-CYC produce two more proteins, PERIOD and TIME (PER-TIM). PER-TIM makes CLK-CYC inactive, as PER-TIM increases CLK-CYC decreases and PER-TIM decreases as well (takes about 24 hours).

3. Critical Point 1: This explanation for the role of the Suprachiasmatic Nucleus is reliable. Morgan bred "mutant" hamsters so they had circadian rhythms of 20 hours instead of 24 hours and then transplanted their SCN's into normal hamsters. He found that the normal hamster displayed the mutant rhythms. Therefore, this implies there is strong evidence to support the theory.

4. Critical Point 2: However, there is a methodological flaw to the majority of the studies carried out on this topic. This is they have been performed on non-human animals. As a result of this, it is difficult to generalise the results displayed by the non-human animals to humans. This is because human beings are far more complex creatures and also systems differ from animal to animal. Also there are serious ethical issues to consider when talking about non-human animals. Although, if we acknowledge that this research does have important applications for human behaviour, then the harm to animals might be considered acceptable as long as the key ethics of non-human animal research remain.

5. Critical Point 3: This explanation has a flaw. Folkard observed a women for 25 days living in a cave. He found that her temperature rhythm was a 24 hour one, but the sleep rhythm was a 30 hour one. Therefore, this implies that body's separate oscillators can desynchronise which can lead to symptoms comparable to jet lag.

6. Critical Point 4: This theory has good evidence. Campell and Murphy found that if you shine a light on the back of the knee, then their circadian rhythms will shift. Consequently, this proves the theory useful as it demonstrates proof that light is the main exogenous zeitgeber.

7. Critical Point 5: There is a negative consequence from the research into the power of artificial lighting. Stevens implies that the exposure to artificial lighting disrupts circadian rhythms and therefore disrupts melatonin production. This could essentially explain why women in industrialised (and well-lit) societies are more likely to develop breast cancer. This is a positive application because it means that we can warn people about the dangers of having lots of lights on all the time.

8. Critical Point 6: There is a negative implication of having a biologically determined system. This is when it fails, it could cause many problems. Chicurel discovered one example of this is Familial Advanced Sleep-Phase Syndrome (FASPS) which has been linked with an inherited defect in one of the PER genes. It seems to cause sleep onset at around 7pm and spontaneous awakening at around 2am in affected family members, and so they have a great difficulty leading a normal life. Therefore this is evidence to support the theory of determinism as you cannot pick your genes.