endogenous pacemakers and exogenous zeitgebers Flashcards
(28 cards)
what is the SCN and where is it located?
a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
The SCN is one of the primary……
endogenous pacemakers
what is the SCN influential in?
maintaining circadian rhythms e.g. sleep/wake cycle
what is the optic chasm?
nerve fibres connected to the eye cross
what does the SCN lie above?
the optic chasm
what type of information does the SCN recieve?
information about light directly from this structure, this continues when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we’re asleep
What did DeCoursey et al do?
destroyed the SCN connections in the brains of 30 chipmunks who were returned to their natural habit and observed for 80 days
what happened to the sleep/wake cycle of the chipmunks?
it disappeared and by the end of the study a significant proportion of them had been killed by predators
what did Ralph et al do?
bred ‘mutant’ hamsters with a 20-hour sleep/wake cycle
What happened when SCN cells from the foetal tissue of mutant hamsters were transplanted?
the cycles of the second group defaulted to 20 hours
what information does the SCN pass to the pineal gland?
information on day length and light
what happens during the night?
the pineal gland increases melatonin
what has melatonin been suggested as a casual factor in?
seasonal affective disorder
endogenous pacemaker evaluation: obscure other body clocks
- research has shown that there are numerous circadian rhythms
- these peripheral oscillators are found in the organs including the lungs
- these are affluence by the actions of the SCN but also independently
- Damiola et al showed how changing feeding patterns in mice could alter the circadian rhythm cells in the liver by up to 12 hours whilst leaving the rhythm of the SCN unaffected
- suggests other complex influences on the sleep/wake cycle
endogenous pacemaker evaluation: cannot be studied in isolation
- total isolation studies e.g. Siffre’s cave study are rare
- siffre also made use of artificial light which could have reset his biological clock every time he turned his lamp on
- in everyday life pacemakers and zeitgebers interact and it may make little sense to separate the two for the purpose of research
- suggests the more researchers attempt to isolate the influence of internal pacemakers the lower the validity of research
what are exogenous zeitgebers?
external factors in the environment that reset our biological clocks through entrainment
What is light in humans?
A key zeitgeber.
what can light reset?
the SCN and plays a role in the maintenance of the sleep/ wake cycle
what does light have an indirect influence on?
key processes in the body that control functions such as hormone secretion and blood circulation
What did Campbell and Murphy demonstrate?
That light may be detected by the skin receptor sites on the body even when the same info isn’t received by the eyes.
What was the procedure of Campbell and Murphy’s study?
- 15 ppts woken at various times.
- Light pad shone on the back of their knees.
What did the researchers manage to produce in Campbell and Murphy’s study?
Managed to produce a deviation in ppts usual sleep/ wake cycle of up to 3 hours in some cases.
What does Campbell and Murphy’s study suggest?
That light is a powerful exogenous zeitgeber that doesn’t need to rely on the eyes to exert its influence on the brain.
What age does the circadian rhythm begin?
6 weeks.
