Biological Rhythms: Circadian Rhythms Flashcards
Biological Rhythms
Governed by endogenous pacemakers & exogenous zeitgebers.
Biological rhythms are periodic activity, governed by:
1) Internal biological ‘clocks’ (endogenous pacemakers).
2) External changes in the environment (exogenous zeitgebers).
Some of these rhythms occur many times a day (ultradian). Others take more than a day to complete (infradian).
Circadian Rhythms
About 1 cycle every 24 hrs - Last for about 24 hrs.
E.g. Sleep/wake cycle.
Sleep/Wake Cycle
Governed by internal & external mechanisms.
1) Endogenous pacemakers - Suprachiasmatic nucleus (SCN) –> signals melatonin production which induces sleep.
2) Exogenous zeitgebers - Light levels signal to the SCN (lies just above the optic chiasm which provides info from the eyes about light) to control levels of melatonin production:
- Less light, more melatonin
- More light, less melatonin
4) Exogenous zeitgebers (light) can reset the sleep cycle.
Case Study - Siffre
Demonstrated a free-running circadian rhythm of about 25 hours.
1) FIRST stay of 61 - circadian rhythm was around 26 hours.
2) SECOND stay of 6 months in cave - just over 24 hours.
3) LAST stay - Ageing on circadian rhythms –> His body clock ticked slowler compared to when he was a young man, sometimes up to 48 hours.
4) Shows natural circadian rhythm is around 24 hours BUT light is important to reset the natural rhythm.
Limitation of Circadian Rhythm
GENERALISATIONS ARE DIFFICULT TO MAKE
1) Studies of the sleep/ wake cycle often use small groups of pps, or even single individuals (e.g. Siffre).
2) Pps may not be representative of the wider population and this limits making meaningful generalisations - Siffre observed that his internal clock ticked slower at 60 than when he was younger.
—> Suggests even when same person is involved, there are factors that may prevent general conclusions being drawn.
Limitation of Siffre
ECOLOGICAL VALIDITY
1) Artifical setting - Most people do not live underground so generalisation is difficult to make to wider population.
Menaker et al.
Importance of SCN in circadian rhythms.
1) Bred a strain of hamsters with abnormal circadian rhythms of 20 hours rather than 24.
2) SCN neurons from abnormal hamsters were transplanted into the brains of normal hamsters.
FINDINGS:
3) Normal hamsters then displayed the same abnormal circadian rhythm of 20 hours.
4) Further confirmation from reverse experiment, planting SCN neurons from normal hamsters into the brains of abnormal hamsters –> Changed to a circadian pattern of 24 hours.
This shows the importance of the SCN in regulating circadian rhythms.
Menaker et al. Evalutation
STRENGTH - Controlled & scientific experiment
LIMITATION - Cannot generalise from animals to humans.
Strength of Circadian Rhythm
REAL-WORLD APPLICATIONS - SHIFT WORK
1) Shift work creates desynchronisation of biological rhythms.
2) Boivin et al. found shift workers experience a lapse of concentration around 6am (a circadian trough) so accidents are more likely.
3) Research also suggests a link between shift work & poor health, with shift workers 3 times more likely to develop heart disease.
—> SO, research into the sleep/wake cycle may have economic implications in terms of how best to manage shift work.
Strength of Circadian Rhythm
REAL-WORLD APPLICATION TO MEDICAL TREATMENT
1) Aspirin reduces heart attacks, which are most likely in the morning. Bonten et al. found taking aspirin is most effective last thing at night.
—> Shows circadian rhythm research can help increase the effectiveness of drug treatments.
