CIRCADIAN RYTHMS
Biological rhythms
Biological rhythms • All living organisms- plants, animals and people- are subject to
biological rhythms and these exert an important influence on the
way in which body systems behave
Endogenous • All biological rhythms are governed by two things- body's internal
pacemakers biological 'clocks', which are called endogenous pacemakers and
Exogenous external changes in the environment known as exogenous zeitgebers
zeitgebers • Some of these rhythms occur any times during the day(ultradian
rhythms)
Ultradian rhythms • Others take longer than a day to complete(Infradian rhythms) and in
Infradian rhythms some cases much longer(circannual rhythms)
• Circadian rhythm last for around 24 hours(circa is Latin for 'about'
Circadian rhythm and diem for 'day'). Two examples of circadian rhythms are the
sleep/wake cycle and core body temperature
The sleep/wake
cycle The sleep/wake cycle
• The fact that we feel drowsy when it's night-time and alert during the
day demonstrates the effect of daylight- an important exogenous
zeitgeber- on our sleep/wake cycle
• However the sleep/wake cycle is also governed by an
internal(endogenous) pacemaker- biological 'clock' called the
suprachiasmatic nucleus(SCN)
• The SCN lies just above the optic chiasm which provides information
from the eye about light
• Exogenous zeitgebers(light) can reset the SCN
• What if the biological clock was 'left to its own devices' without the
influence of external stimuli such as light
Michel Siffre
Siffre's cave study
• Michel Siffre is a self-styled caveman who has spent several
extended periods underground to study the effects on his. Own
biological rhymes
• Deprived of exposure to natural light and sound, but with access to
adequate food and drink, Siffre resurfaced in mid-September 1962
after two months in the caves of the Southern Alps believing it to the
mid-August
• A decade later he performed a similar fear to a 'free-running'
• If we had no idea whether it was night or day would we still fall
Jurgen Aschoff and asleep and wake up at regular times?
Rutger Wever(1976) • Research have tried to answer this question
Other research
• Similar results recorded by Jurgen Aschoff and Rutger Wever(1976)
who convinced a group of participants to spend four weeks in a
World War 2 bunker deprived of natural light
• All but one of the participants(whose sleep/wake cycle extended to
29 hours) displayed a circadian rhythm between 24 and 25 hours
• Both Siffre's experience and the bunker study suggest that the
'natural' sleep/wake cycle may be slightly longer than 24 hours but
Biological rhythms
Biological rhythms • All living organisms- plants, animals and people- are subject to
biological rhythms and these exert an important influence on the
way in which body systems behave
Endogenous • All biological rhythms are governed by two things- body's internal
pacemakers biological 'clocks', which are called endogenous pacemakers and
Exogenous external changes in the environment known as exogenous zeitgebers
zeitgebers • Some of these rhythms occur any times during the day(ultradian
rhythms)
Ultradian rhythms • Others take longer than a day to complete(Infradian rhythms) and in
Infradian rhythms some cases much longer(circannual rhythms)
• Circadian rhythm last for around 24 hours(circa is Latin for 'about'
Circadian rhythm and diem for 'day'). Two examples of circadian rhythms are the
sleep/wake cycle and core body temperature
The sleep/wake
cycle The sleep/wake cycle
• The fact that we feel drowsy when it's night-time and alert during the
day demonstrates the effect of daylight- an important exogenous
zeitgeber- on our sleep/wake cycle
• However the sleep/wake cycle is also governed by an
internal(endogenous) pacemaker- biological 'clock' called the
suprachiasmatic nucleus(SCN)
• The SCN lies just above the optic chiasm which provides information
from the eye about light
• Exogenous zeitgebers(light) can reset the SCN
• What if the biological clock was 'left to its own devices' without the
influence of external stimuli such as light
Michel Siffre
Siffre's cave study
• Michel Siffre is a self-styled caveman who has spent several
extended periods underground to study the effects on his. Own
biological rhymes
• Deprived of exposure to natural light and sound, but with access to
adequate food and drink, Siffre resurfaced in mid-September 1962
after two months in the caves of the Southern Alps believing it to the
mid-August
• A decade later he performed a similar fear to a 'free-running'
• If we had no idea whether it was night or day would we still fall
Jurgen Aschoff and asleep and wake up at regular times?
Rutger Wever(1976) • Research have tried to answer this question
Other research
• Similar results recorded by Jurgen Aschoff and Rutger Wever(1976)
who convinced a group of participants to spend four weeks in a
World War 2 bunker deprived of natural light
• All but one of the participants(whose sleep/wake cycle extended to
29 hours) displayed a circadian rhythm between 24 and 25 hours
• Both Siffre's experience and the bunker study suggest that the
'natural' sleep/wake cycle may be slightly longer than 24 hours but
