Endogenous Pacemakers and Exogenous Zeitgebers Flashcards
What are endogenous pacemakers?
Internal body clocks that regulate biological rhythm
What is the superchiasmatic nucleus (SCN)?
Bundle of nerve cells
Where is the SCN located?
Hypothalamus
What is the SCN linked with?
The sleep/wake cycle
What is the SCN connected to?
Optic chiasm
What does the SCN receive?
Light directly when the eyes are closed
Which two psychologist researched into the sleep/wake cycle?
- Decoursey et al
- Ralph et al
What did Decoursey et al (2002) do?
- Destroyed SCN connection in 30 chipmunks
- Returned them to natural habit and observed
What did Decoursey et al (2000) find?
Sleep/wake cycle disappeared and majority killed after 80 days
What did Ralph et al (1990) do?
- Bred hamsters with 20 hour sleep/wake cycle
- SCN of mutant hamsters transplanted into normal hamsters
What did Ralph et al (1990) find?
Normal hamsters developed a 20 hour sleep/wake cycle
What is the SNC an example of?
Endogenous pacemaker
What are the three examples of endogenous pacemaker?
- SCN
- Pineal gland
- Melatonin
How is SCN linked to the pineal gland and melatonin?
SCN passes information on day length to pineal gland which increases secretion of melatonin during the night
What does melatonin induce?
Sleep
When is melatonin inhibit?
During periods of wakefulness
What are the different factors which influence the sleep/wake cycle?
- Endogenous pacemakers
- Exogenous zeitgebers
What are exogenous zeitgebers?
External cue which may affect biological rhythm i.e reset the biological clock
What is the resetting of the biological clock is a process known as?
Entrainment
What important exogenous zeitgebers are involved in the sleep/wake cycle?
- Light
- Social cues
Who studied into the effect of light on the sleep/wake cycle?
Campbell and Murphy (1998)
What did Campbell and Murphy (1998) do?
- Woke 15 participants at various times
- Shone a light on backs of their knee
Why did Campbell and Murphy (1998) shine a light on the backs of their participants knees?
Produces a deviation in the sleep/wake cycle
Does the detection of light just occur by the SCN?
No - skin receptors can also detect light
How has social cues shown to be an important influence on sleep/wake cycle?
- Babies have set schedules can set sleep/wake cycle (normally really random in newborns)
- Adapting to local time when travelling for eating and sleeping resets circadian rhythm (tackles jet lag)
Is SCN the only endogenous pacemaker?
No
What are other endogenous pacemakers?
- Lungs
- Liver
- Skin
- Pancreas
Why is studies into SCN limiting?
As ignores the important and the independence of the effects of other endogenous pacemakers
Who showed the independence of the liver to the SCN?
Damiola et al (2000)
What did Damiola et al (2000) find?
That altering feeding pattern altered circadian rhythm of the liver of up to 12 hours
Are you able to generalise animal studies to humans?
No
What are the issues when studying SCN and animal studies?
- Ethical issues
- Great harm and potential risk when returned back to habitat
How may the influence of exogenous zeitbegebers be overstated?
People who are born bind show normal sleep/wake cycle, only needed to take sedatives in the morning to align with 24-hour world (Miles et al. 1977)
What was a limitation to Campbell and Murphy (1998) method?
- Hasn’t been replicated
- Some light exposure to participants eyes (confounding variables)
What may studies have ignored when studying into exogenous zeitebegers?
How different exogenous zeitbegers interact and influence the sleep/wake cycle (reductionist)
What is the collective problem between the research in to exogenous zeitebegers and endogenous pacemakers?
- That it is hard to separate the two when conducting research into just one
- Why do researchers try to separate the two functions when they work together
