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Biological Rhythms: Circadian Rhythms - Coggle Diagram
Biological Rhythms: Circadian Rhythms
Biological Rhythms
all living organisms are subject to
biological rhythms
& theses exert an importance influence on the way in which body systems behave
all biological rhythms are controlled by 2 things:
(1) the body's internal Biological clocks [called
endogenous pacemakers
]
(2) external changes in the env [called
exogenous zeitgebers
]
some of these rhythms occur multiple times during the day [
ultradian rhythms
] whereas other take longer than a day to complete [
infradian rhythms
]. sometimes even longer [
Circannual rhythms
]
Circadian Rhythms
are those rhythms that last for around 24 hours ['circa' is latin for 'about' and 'diem' for 'day']
The Sleep/wake cycle
feeling of drowsy at night & alert during day shows effect of daylight [important exogenous zeitgeber] on our sleep/wake cycle
but sleep/wake cycle is also governed by and internal [endogenous pacemaker] biological clock called the
suprachiasmatic nucleus (SCN)
SCN is situated just above the
optic chiasm
which provides info from the eye about light
exogenous zeitgeber (light) can reset the SCN
Siffre's Cave study
Michael Siffre is a self-styled caveman who's spent several extended periods of time underground to study effects of his own biological rhythms
deprived exposure to natural light, sound, but with access to adequate food & water
Siffre resurfaced in mid-september 1962 after 2 months in the caves of the Southern Alps.
a decade later he performed similar feat but this time for 6 months in a Texan cave.
in each case, his 'free-running' biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule
other research
similar results were recorder by
Jurgen Aschoff and Rutger Wever1976
who convinced a group of ppts to spend 4 weeks in a WW2 bunker deprived of natural light
all but 1 ppts (whos sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24-25 hours
both Siffre's experience and the bunker study suggest the 'natural' sleep/wake cycle is a little over 24 hours but that it is entrained by exogenous zeitgebers associated without our 24-hour day (e.g. daylight hours, mealtimes etc.)