Endogenous pacemakers & Exogenous zeitgebers Flashcards

1
Q

What are endogenous pacemakers?

A

Internal body clocks that regulate biological rhythms e.g. influence of SCN on the sleep/wake cycle

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2
Q

What is the suprachiasmatic nucleus (SCN)?

A
  • a tiny bundle of nerve cells located in the hypothalamus in each hemisphere which is one of the primary endogenous pacemakers in mammals
  • is influential in maintaining circadian rhythms like sleep/wake cycle
  • receives info about light directly from optic chiasm which enables biological clock to adjust
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3
Q

What was DeCourcy et al’s (2000) study?

A
  • influence of SCN demonstrated
  • SCN in 30 chipmunks were destroyed before returning to their natural habitat and being observed for 80 days
  • sleep/wake cycle of chipmunks disappeared and by the end of the study a significant number were killed by predators since they were awake and vulnerable to attack instead of sleeping
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4
Q

How does the pineal gland contribute to the sleep/wake cycle?

A
  • it receives info from SCN about the day length & light
  • during the night the pineal gland increases production of melatonin which induces sleep and is inhibited during period of wakefulness
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5
Q

What are exogenous zeitgebers?

A

External cues that may affect our biological rhythms e.g. the effect of light on the sleep/wake cycle

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6
Q

How does light work as an exogenous zeitgeber?

A
  • resets the SCN and therefore plays a role in the maintenance of the sleep/wake cycle
  • also has an indirect influence on key processes in the body that control hormone secretion & blood circulation for e.g.
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7
Q

How do social cues work as an exogenous zeitgeber?

A
  • the initial sleep/wake cycles of human infants are pretty random so schedules are imposed by parents are likely to be the key influence
  • research also suggests that adapting to local times for eating
    sleeping is an effective way of training circadian rhythms
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8
Q

Evaluation: Beyond the master clock

A
  • research revealed that there are many circadian rhythms in many organs and cells in the body
  • these are called peripheral oscillators found the the adrenal gland, lungs, liver etc
  • although peripheral clocks are highly influenced by SCN they can act independently
  • Damiola et al demonstrated how changing feeding patterns in mice could alter circadian rhythms of liver cells whilst SCN rhythm is unaffected
  • this suggests that there may be many other complex influences on sleep/wake cycle other than the SCN
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9
Q

Evaluation: Ethics in animal studies

A
  • particularly in relation to DeCoursey et al’s study issue of ethics is raised
  • animals were exposed to considerable harm and put at risk to predators in their natural habitat
  • whether knowledge gathered from these studies is justified is a matter of debate
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10
Q

Evaluation: Influence of exogenous zeitgebers may be overstated

A
  • Miles et al recount of a man blind from birth with a circadian rhythm of 24.9 hours
  • despite exposure to social cues his sleep/wake cycle couldn’t be adjusted so he had to take sedatives at night & stimulants in the morning to keep pace with the 24-hour clock
  • this suggests that there are occasions when exogenous zeitgebers may have a little bearing on our internal rhythm
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11
Q

Evaluation: Interactionist system

A
  • only in exceptional circumstances are endogenous pacemakers free-running & unaffected by exogenous zeitgebers
  • total isolation studies (Siffre) are very rare and could be judged as lacking validity
  • in real life pacemakers & zeitgebers interact and make little sense to separate for research
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