exogenous zeitgebers & endogenous pacemakers

aqa a level psychology biopsychology

what are exogenous zeitgebers?

what are exogenous zeitgebers?

external cues from the environment that entrain our endogenous rhythms

what are examples of exogenous zeitgebers?

• light

• temperature

• meal times

what social cues are exogenous zeitgebers?

• mealtimes

• social activities

who studied jet lag as an exogenous zeitgeber?

klein & wegmann

what was klein & wegmann’s procedure?

• studied air travellers

• exposed to social cues of new time zones

what did klein & wegmann find?

• circadian rhythms are better explained in terms of light exposure

• connections exist between the eye and the SCN

• air travellers adjusted faster if they went outside at their new destination

how is light an exogenous zeitgeber?

• receptors in the SCN are sensitive to light

• use this to synchronise organs & glands

• light resets biological clocks

• 3rd type of light detecting cell in retina gauges overall brightness

• protein is critical in this system to carry signals to the SCN

what are endogenous pacemakers?

internal body clocks that regulate many of our biological rhythms

what is the SCN?

the primary pacemaker in the brain

where is the SCN?

the hypothalamus

what does the SCN do?

• helps other areas maintain regular circadian rhythms

• has internal time management system based on complex cellular process

how is light & the SCN connected?

• 3rd type of light receptor in retina sends the protein melanospin to the SCN

• SCN communicates with pineal gland

• increases melatonin in absence of light

  • inhibits melatonin in presence of light

what did decoursey et al find?

destroying the SCN causes the sleep/wake cycle to disappear

what are the issues with decoursey et al?

• chipmunks died

• small sample used (30)

• animal sample

what did ralph et al find?

SCN cells from mutant hamsters in the brain of normal ones reset the cycle to 20 hours

what are the issues with ralph et al?

• bred mutant hamsters

• animal sample

what did campbell and murphy find?

skin can detect light & affect sleep/wake cycles

what are the issues with campbell & murphy?

• only 15 pps

what are the issues with klein & wegmann?

• limited sample size

what did siffre find?

biological rhythms settle to 25 hours without light

what are the issues with siffre?

• limited sample size

• biological rhythms change with age

what did aschoff & weaver find?

biological rhythms extended and the natural rhythm is longer than 24 hours

what are the issues with aschoff & weaver?

• small sample

• entrained by exogenous zeitgebers

what did mcclintok et al find?

exposure to irregular cycle hormones influence the receivers cycle

what are the issues with mcclintok et al?

• unhygeinic

• small sample

• 3 statistical errors

• sampling bias

what are the strengths of research into exogenous zeitgebers and endogenous pacemakers?

• numerous circadian rhythms - peripheral oscillators - adrenal gland, oesphagus, lungs, liver, pancreas, spleen, thymus, skin - influenced by SCN - Damiola et al - changing feeding patterns in mice after CR in liver - suggests more complex influences

what are the weaknesses of research into exogenous zeitgebers and endogenous pacemakers?

• ethical issues - animal studies - hard to generalise - DeCoursey et al - considerable harm & risk - not worth the risk - also can’t use humans

• influence may be overstated - Miles - recounts story of blind man with circadian rhythm of 24.9 hours - despite exposure to social cues - stimulants + sedatives needed - people in midnight sun regions show normal patterns - occasions where ez has little influence