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Flashcards in Endogenous And Exogenous Pacemakers Deck (13)
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1

What are endogenous pacemakers ?

Internal body clocks that regulate many of our biological rhythms such as the influence of the suprachiasmatic nucleus (SCN) on the sleep- wake cycle.

Affected by the enviroment
Can function without cues from the enviroment - alters circadian rhythm

2

What is an example of an endogenous pace maker

The Suprachiasmatic Nucleus (SCN) and the Pineal Gland

3

Explain the suprachiasmatic nucleus

This is an endogenous pacemaker.
• It is located in the hypothalamus.
• It is influential in maintaining circadian rhythms.
• It is regulated by light from the environment. It receives information about light, even when eyes
are closed.
• It passes information on day lengths and light to pineal gland.
• During the night the pineal gland produces melatonin. This is a chemical inducing sleep and is
inhibited during periods of wake.

4

Explain Ralph et als study

Created ‘mutant’ hamsters who had a 20 hour sleep-wake cycle.
• Transplanted the SCN cells from the mutant hamsters into the brains
of normal hamsters (24 hour sleep-wake cycle).
• The normal hamsters following transplantation ended up on a 20 hour sleep-wake cycle.
• This shows the role of the SCN in establishing and maintaining the sleep-wake cycle.

5

Explain exogenous zeitgebers

external cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep wake cycle.

Zeitgebers synchronise our body to the enviroment

free running body clock, when there are no external cues, we have a sleep-wake cycle, but it is not 24 hours. External and internal cues work together to determine our 24-hour cycle.

6

What is the effect of light

resets the SCN. It also affects hormone secretion and blood circulation

7

Outline Campbell and Murphy into light

Showed light can be detected by skin receptors on body
Even if same information not received by eyes

15 participants woken up at various times - light shone on back of knees

Produced a deviation in participants usual sleep wake cycle

Suggests light is a powerful exogenous zeitgebers influences our Brain and body

8

Explain social cues

schedules that are imposed on us by society and are key influences on our sleep wake cycle e.g. times to eat, times to go to bed. Entrainment of the body following jet lag is quicker when people eat and sleep when the local culture do, rather than responding to your own body and feelings of hunger and fatigue.

9

Explain strength of zeitegabers

Draws away attention from other body clocks.

Circadian rhythms in many organs and cells

Eg peripheral oscillators - in adrenal gland , throat , lungs skin and pancreas

Research showed changing feeding pattern in mice altered circadian rhythms for 12 hours in the liver- rhythm of SCN unaffected

Complex influences on sleep/wake aside from master clock

10

What is a limitation of research into zeitegabers (animal studies)

Use animals to research
Generalising findings from research from animal studies
Problematic

Cog factors in human different
Ethical issues - decourseys study
Animals exposed to great harm
The benefit of research into biological rhythms may not justify cost of adverse processes.

11

What is a limitation of exogenous zeitegabers

The influence of exogenous zeitgebers may be overstated.
Individuals who live in Arctic regions (where the sun does not set during the summer months) show normal sleep patterns despite prolonged exposure to light

. This suggests there are occasions when exogenous zeitgebers may have little bearing on our internal rhythms.

12

What is another limitation of exogenous zeitegabers (methological issues with research)

Campbell and Murphy’s study (1998) has yet to be replicated

criticised because there may have been some light exposure to participant’s eyes - a major confounding variable.

Also, isolating one exogenous zeitgeber (light)
Doesn’t take in account other zeitgebers that influence the sleep/ wake cycle.

suggests that some studies may have ignored or underplayed the way in which different exogenous zeitgebers interact.

13

What is a strength of endogenous zeitegabers (cause and effect)

Animal studies - cause and effect

DeCoursey’s study
chipmunks had their SCN connections destroyed and were then released into their habitat.
inability to function -> had happened to their SCN.

unethical to conduct with humans
wouldn mean that we would not know about the effect of the SCN on the sleep-wake cycle had this research not been completed.