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
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
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
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
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
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.
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
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
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
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
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