Exogenous & Endogenous Factors Flashcards
Define endogenous pacemakers
Part of internal organism; internal body clock which regulates biological rhythms such as sleep/wake cycle
Define exogenous zeitgebers
External cues in the environment which may affect biological rhythms
How do exogenous zeitgebers work?
Biological clock reset everyday by cues in the environment (sunrise/set)
~ process = entrainment; works according to exogenous cues
Describe light as an exogenous zeitgeber
SCN (suprachiasmatic nucleus) contains receptors which are reactive + sensitive to light; used to synchronise body’s internal organs + glands
Describe social cues as exogenous zeitgeber
Initially random at birth, but babies quickly become entrained (~16 weeks)
~ from schedules and cues from parents e.g. mealtimes/bedtimes
Outline animal research into endogenous pacemakers
Decoursey —> destroyed SCN connections in chipmunks + returned to natural habitat; found most were quickly killed by predators as they had left their nests at the wrong time of day
Ralph et al —> bred mutant hamsters with 20h sleep/wake cycle; found when SCN was transferred to normal hamsters, cycle of 2nd group defaulted to 20hrs
- shows changes to SCN alter the sleep/wake cycle BUT difficult to generalise to humans
Evaluate endogenous pacemakers
Reductionism —> suggests SCN is only endogenous pacemaker responsible for sleep/wake cycle when research has demonstrated peripheral oscellators also affect sleep/wake cycle
Interactionism —> cannot study endogenous pacemakers in isolation; makes little sense to separate zeitgebers + pacemakers as interact in real life
Issues with case study evidence —> impossible to generalise these to the whole population as individual differences could impact changes in sleep/wake cycle
What is our main endogenous pacemaker and how does this detect light?
Suprachiasmatic nucleus —> cluster of nerve cells found in hypothalamus
- light penetrates eyelids and photoreceptors in the eye transfer light signals to the SCN
How is melatonin secreted in response to light?
Secreted by pineal gland
- contains light-sensitive cells
- when light is detected, melatonin prod is inhibited
- when light levels fall, melatonin prod increases as melanopsin carries signals to the SCN
- induces sleep by inhibiting brain mechanisms promoting our awake state
Evaluate exogenous zeitgebers
Practical application —> jet lag
- Burgess found exposure to bright light after an east-west flight decreases time needed to adjust to local time
- exposed to either continuous bright, intermittent bright or dim light; continuous shifted circadian rhythm back 2.1hrs vs 0.6 in dim
- demonstrated how we can entrain our circadian rhythms to reduce jet lag
Environmental differences —> people living in places w little darkness in summer + little light in summer (I.e. Arctic circle) exhibit similar sleep patterns year-round despite light changes
- suggests endogenous pacemakers able to override external influences
- also not as influential in certain people, individual differences
Outline research supporting exogenous zeitgebers
Camobell & Murphy - 15 pptswere woken at various times during the night + light shone on back of the knee
- researchers able to alter sleep/wake cycle by up to 3 hrs
- supports idea of light as a powerful zeitgeber
