13. Biological Rhythms: Circadian Rhythms AO1 Flashcards
What are biological rhythms?
Periodic activity
What are biological rhythms governed by?
- Internal biological ‘clocks’
2. External changes in the environment
What are internal biological ‘clocks’ called?
Endogenous pacemakers
What are external changes in the environment called?
Exogenous zeitgebers
When do rhythms occur?
Ultradian rhythms - many times a day
Infradian rhythms - take less than a day to complete
Circannual rhythms - much longer
How many important types of circadian rhythms are there
Several such as sleep/wake cycle
Explain exogenous zeitgebers
The fact we feels drowsy when it’s night-time and alert during day-time shows the effect of daylight
Explain endogenous pacemakers
A biological ‘clock’ left to its own devices without the influence of external stimuli (e.g. Light) is called free-running
Explain the idea of there being a basic rhythm
It’s governed by the suprachiasmatic nucleus (SCN), which lies just above optic chaise and receive information about light.
What can exogenous zeitgebers do to the SCN
Reset it
What did Siffre do?
Spent long periods in dark caves to examine the extent of free running biological rhythms
Where did Siffre stay?
- Two months in caves in the Southern Alps
- Six months in a Texan cave
What did Siffre demonstrate?
Free-running circadian rhythms of about 25 hours
What is important to remember about Siffre?
He did have a regular sleep/wake cycle
Who found a similar circadian rhythm?
Aschoff and Wever
What did Aschoff and Wever do?
A group of participants spent four weeks in a World War II bunker deprived of natural light
What did Aschoff and Wever find?
All but one display a circadian rhythm between 24 and 25 hours
What did the research suggest
Siffre and Aschoff’s research suggested the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with out 24- hour day
What may endogenous pacemakers have?
Stronger influence than exogenous zeitgebers
Who did Folkard et al study and what was the procedure?
A group of 12 people who lived in a dark cave for three weeks, going to bed 1 o’clock said 11:45 PM and waking when it said 7:45 AM
What did Folkard et al change?
Research is gradually speeded up the clock so an apparent 24 hour day eventually lasted only 22 hours
What did Folkard et al find?
Only one participant comfortably adjusted to
What does Folkard et al’s study suggest?
A strong free running circadian rhythm cannot easily be over written by changes in external environment
