Biological rhythms- endogenous pacemakers

Question 1

What are endogenous pacemakers?

Answer 1

Internal body clocks found in the hypothalamus called the suprachiasmatic nucleus (SCN) and synchronises the sleep/ wake cycle circadian rhythm.

Question 2

Explain the role of endogenous pacemakers in the sleep/ wake cycle.

Answer 2

1. SCN receives light through the eyes
2. When light levels drop, this information is received by the SCN, causing it to fire impulses to the pineal gland which secretes melatonin, causing sleepiness.
3. When light increases, melatonin levels fall, making us more alert.
4. Without light as a zeitgeber, the process ‘free runs’ to a 25 hour cycle.

Question 3

If the point is:

A strength of endogenous pacemakers is that there is case study evidence to support the role them in regulating circadian rhythms like the sleep/ wake cycle.

What is the evidence and link?

Answer 3

Evidence- For example, Siffre spent 6 months in an underground cave in Texas, separated from natural light/ dark cycles. This allowed him to investigate what happens when the bodily sleep/ wake cycle is allowed to ‘free run’ away from exogenous zeitgebers. He was wired up so various bodily functions could be recorded and ate and slept whenever he wanted. At first, his sleep/ wake cycle was very erratic, but settled down to a fairly regular pattern of between 25/30 hours- slightly longer than 24 hour cycle.

Link- This supports the idea that endogenous pacemakers are important in regulating this rhythm, but also suggest that exogenous zeitgebers play a role too.

Question 4

If the point is:

A weakness of endogenous pacemakers is that many studies into the effects on humans come from case studies such as the Siffre study.

What is the evidence, explanation and link?

Answer 4

Evidence- For example, the experiment was only done on 1 person, so cannot be generalised, as there was no large sample. Also, everybody has a biological rhythm and this area of research affects the whole purpose.

Explanation- This means we should be cautious when applying findings, as they aren’t generalisable to the whole population.

Link- Therefore, this research may not provide credible evidence for the role of endogenous pacemakers in controlling circadian rhythms.

Question 5

If the point is:

Another strength of endogenous pacemakers is that there’s more scientific evidence to support their role in regulating circadian rhythms like the sleep/ wake cycle from animal studies.

What is the evidence and link?

Answer 5

Evidence- For example, Ralph et al took the SCN from a ‘mutant hamster’ who had a circadian rhythm which had mutated to 20 hours. They transplanted the mutant SCN into the brains of normal adult hamsters which then took on the circadian rhythms of mutant hamsters.

Link- This shows the importance of the SCN in being responsible for our sleep cycle.

Question 6

If the point is:

However a weakness of endogenous pacemakers is that the use of animal studies may be problematic when considering their role in human circadian rhythms.

What is the evidence and link?

Answer 6

Evidence- For example, there may be problems when generalising the findings from animals to humans, as humans are more advanced and have denser brains, whereas hamsters are more simplistic.

Link- This means that the research may not be fully helpful when being used to explain endogenous pacemakers in humans

Question 7

What are the evaluations of endogenous pacemakers?

Answer 7

+ There is case study evidence to support their role in regulating circadian rhythms like the sleep/wake cycle

— Many studies into the effects on humans come from case studies like the Siffre study

+ There’s more scientific evidence to support their role in regulating circadian rhythms like the sleep/ wake cycle from animal studies

— The use of animal studies may be problematic when considering the role of endogenous pacemakers in human circadian rhythms