10._Endogenous_Pacemakers_and_Exogenous_Zeitgebers.pptx

psychology prseentation

1. Starter Outline the stages of sleep Describe the menstrual cycle and how it can become synchronised with other females

2. Endogenous Pacemakers and Exogenous Zeitgebers Miss Mendonca [email protected]

3. Specification

4. Example of an endogenous pacemaker influencing sleep/wake cycle : Example of an exogenous zeitgeber influencing sleep/wake cycle : Suprachiasmatic Nucleus (SCN), which lies in the hypothalamus Light: This is the key zeitgeber and Social cues A01

5. Endogenous Pacemakers (AO1)

6. Tiny bundle of nerves in the hypothalamus in both hemispheres Primary endogenous pacemaker in mammals and regulates many circadian rhythms Lies just above the optic chiasm (crossing point for nerves in eye on their way to visual cortex) Receives information about light from the optic chiasm, even when eyes are shut which lets the biological clock adjust to different levels of daylight even when we are asleep The Suprachiasmatic Nucleus (AO1)

7. Pineal gland secretes the hormone melatonin I nformation about day length and light is passed from the SCN to the pineal gland (small structure behind the hypothalamus) Night time = increased secretion of melatonin Day time = reduced secretion of melatonin The Pineal Gland (AO1)

8. DeCoursey et al. (2000) Destroyed SCN connections in 30 chipmunks Returned chipmunks to natural habitat and observed for 80 days At end of study significant proportion had been killed by predators Ralph et al. (1990) Bred ‘mutant’ hamsters with 20-hour sleep/wake cycle SCN cells from foetal tissue of mutant hamsters transplanted in brains of normal hamsters Sleep/wake cycle of normal hamsters defaulted to 20 hours Studies on SCN (AO1) How can we evaluate these studies? How can we explain these findings ?

9. Evaluation (AO3)

10. Beyond the Master Clock (AO3) Is the ‘master clock’ (SCN) our body’s only internal biological clock? What evidence is there to answer the above question?

11. Beyond the Master Clock (AO3) Peripheral oscillators located on other organs, influenced by SCN but act independently Damiola et al. (2000) changing feeding patterns in mice could change circadian rhythms for up to 12 hours but the SCN was unaffected

12. Interactionist System (AO3) Endogenous pacemakers cannot be studied in isolation as it is very unlikely- if not impossible- that exogenous zeitgebers will not be present Even in the Siffre (cave study), artificial lights were used so it could be argued that when Siffre’s biological clocks were being influenced when the artificial lights were being turned them on/off This demonstrates that endogenous pacemakers and exogenous zeitgebers interact so it may not make sense to separate them for the purposes of research

13. Ethics (AO3) Several studies on animals have been conducted that have shown the influence of the SCN – DeCoursey et al (2000) – destroyed the SCN connections in the brains of 30 chipmunks Ralph et al – bred ‘mutant’ hamsters with a 20 hour sleep cycle What ethical issues did these studies have? Protection from harm Lack of informed consent

14. Exogenous Zeitgebers (AO1)

15. E xternal factors in the environment that reset our biological clocks through entrainment Examples = Light and Social Cues In the absence of external cues, the ‘free-running’ biological clock allows the sleep/wake cycle to continue in a cyclical pattern (as evidenced by the Siffre study) This ‘free-running’ is then controlled by external factors (i.e. exogenous zeitgebers), showing the interaction between internal and external influences Exogenous Zeitgebers (AO1)

16. Task! (AO1) In pairs, label yourselves A and B. A: Light B: Social cues Take notes on your section and teach your partner what you’ve learned

17. Can reset the SCN by entrainment so can affect the sleep/wake cycle Can have indirect influence on processes such as hormone secretion and blood circulation Campbell and Murphy (1998) Light could be detected by receptors on the skin even if the eyes cannot detect this information 15 participants were woken up at several points and had a light pad shone to the backs of their knees. In some cases, this caused a deviation of up to 3 hours in some of their sleep/wake cycles This demonstrates the importance of light as an exogenous zeitgeber that does not necessarily rely on the eyes for it to be influential Light (AO1) Entrainment: The process that activates or provides a timing cue for a biological rhythm

18. Infants do not exhibit a rhythmic sleep/wake cycle (usually quite random to begin with) Entrainment begins at around 6 weeks old as a result of parental influence on meal times and bedtimes and this is usually solidified by about 16 weeks old Jet lag can be tackled by taking advantage of social cues (adapting to local eating and sleeping times immediately can help to beat jet lag more quickly Social Cues (AO1)

19. Evaluation (AO3)

20. Environmental Observations (AO3) A limitation is that exogenous zeitgebers do not have the same effect in all environments (i.e. those who live in countries with extreme levels of light or darkness) Those who live in the Arctic Circle (e.g. Greenland) have similar patterns all year round despite spending about 6 months in complete darkness This suggests that endogenous pacemakers have more control over biological rhythms and can override environmental changes

21. Case Study Evidence (AO3) Miles et al. (1977) recount the story of a young man, blind from birth with a circadian rhythm of 24.9 hrs. Despite exposure to social cues, his sleep wake cycle could not be adjusted and, consequently, he had to take sedatives at night and stimulants in the morning to keep pace with the 24 hour world Why would it be that he had an unusual rhythm? (think about EZ's - he's blind) What else does this tell you about the influence of EZ's?

22. Age-related Insomnia ( AO3) Evidence suggests that people have poorer quality sleep as they get older (30% of people over 60 have chronic insomnia). This may be due to natural changes in the body's circadian rhythm as we age, which can result in falling asleep earlier in the evening and the experience of broken sleep during the night (Duffy et al. 2015). The usual response to this is medication to increase melatonin levels (sleeping tablets) However, Hood et al. (2004) found that management of insomnia was improved if elderly people were generally more active and had more exposure to natural light by going out during the day, suggesting exogenous zeitgebers are more responsible for the changes in sleeping patterns with age.

23. Plenary- consider how marks would be allocated! Julia complains that her baby is sleeping all day and keeping her awake all night. Using your knowledge of research into exogenous zeitgebers, discuss what Julia could do to encourage her baby to sleep more at night. (8 marks)