Endogenous pacemakers & Exogenous zeitgebers Flashcards
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.
What is the sleep/wake cycle?
A daily cycle of biological activity based on a 24-hour period that is influenced by regular variations in the environment, such as the alternation of night and day.
What is the SCN and where is it located (broadly)?
It is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
Write a paragraph describing DeCoursey et al’s study. (rats)
-DeCoursey et al. (2000) destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days.
-The sleep/wake cycle of the chipmunks disappeared.
By the end of the study a significant proportion of them had been killed by predators.
Write a paragraph describing Ralph’s study. (hamsters)
-Ralph (1990) bred ‘mutant’ hamsters with a 20 hour sleep/wake cycle.
-When SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours.
What is an exogenous zeitgeber?
External factors that affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle.
What does zeitgeber mean?
Time giver.
What happens in the absence of external cues?
The free-running biological clock that controls the sleep/wake cycle continues to ‘tick’ in a distant cyclical pattern.
Write a paragraph describing Campbell and Murphy’s study. (light)
-Campbell and Murphy (1998) demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by the eyes.
-15 participants were woken at various times and a light pad was shone on the back of their knees.
-The researchers managed to produce a deviation in the participants’ usual sleep/wake cycle of up to 3 hours in some cases.
-This suggests that light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert its influence on the brain.
How can you reduce the symptoms of jet lag?
By adapting to local times for eating and sleeping (rather than responding to ones own feelings of hunger and fatigue) is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances.
When does the sleep/wake cycle start to begin in newborns?
About 6 weeks.
What happens to a babies sleep/wake cycle at around 16 weeks?
The rhythms have been entrained by the schedules imposed by parents, including meal times and bedtimes.
Write a PEEL paragraph about the limitation about endogenous pacemakers:
Beyond the master clock.
P: One limitation of SCN research is that it may obscure other body clocks.
E: Research has revealed that there are numerous circadian rhythms in many organs and cells in the skin. These peripheral oscillators are found in the organs including the lungs, pancreas and skin. These are influenced by the actions of the SCN, but also act independently.
E: Damiola et al. (2000) demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
L: This suggests other complex influences on the sleep/ wake cycle.
Write a PEEL paragraph on the limitation about endogenous pacemakers:
Interactionist system.
P: One limitation is that endogenous pacemakers cannot be studies in isolation.
E: Total isolation studies (e.g. Siffre) are extremely rare. Siffre also used artificial light which could have reset his biological clock every time he turned his lamp on.
E: In everyday life pacemakers and zeitgebers interact and it may make little sense to separate the 2 for the purpose of research.
L: This suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of research.
Write a PEEL paragraph on the limitation about exogenous zeitgebers:
Environmental observations.
P: One limitation is that exogenous zeitgebers do not have the same effect in all environments.
E: The experience of people who live in places where there is very little darkness in summer and very little light in winter tell a different story from the usual narrative.
E: People who live in the Arctic Circle have similar sleep patterns all-year round, despite spending around 6 months in almost total darkness.
L: This suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light.
