Flashcards in Endogenous And Exogenous Pacemakers Deck (13)
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
What is an example of an endogenous pace maker
The Suprachiasmatic Nucleus (SCN) and the Pineal Gland
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
• 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.
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.
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.
What is the effect of light
resets the SCN. It also affects hormone secretion and blood circulation
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
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.
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
What is a limitation of research into zeitegabers (animal studies)
Use animals to research
Generalising findings from research from animal studies
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.
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.
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.