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What type of rhythm is a Circadian Rhythm
Biological Rhythm
What cycle does the Circadian Rhythm meet the demands of
The Day/Night Cycle
What are Circadian Rhythms controlled by and where is it located
The master circadian pacemaker in the hypothalamus
What sensory organ detects light
The eyes
What are three examples of Circadian Rhythms
Sleep Wake Cycle
Body temperature
Hormone production
Levels of body temperature throughout the day
Lowest = 4:30 am
Highest = 6:00 pm
What two times do CR dip
2-4am
1-3pm (post lunch dip)
When is sleepness in dips less intense
When we have sufficient sleep
What other function can also controls sleep and wakefulness
Homeostasis
What will the internal circadian clock maintain even in the absences of light
a 24-25 hr cycle
What are CR intolerant to
Major sleep altercation eg Jet lag
Siffre
He spent long periods underground with no external cues (daylight, clocks, radio) to guide his rhythm, but his internal body clock was still running.
Findings: 61 days underground (believed it was 33 days)
A later underground stay at age 60 (37 years after his first stay), Siffre wanted to test the effects of ageing on circadian rhythms.
Findings: his body clock was slower than when he was younger.
Who tested circadian hormone release in 4 ppts stationed in the British Antarctic Station (AO3)
Hughes
Research support for the importance of light (AO3)
Hughes tested circadian hormone release in 4 ppts stationed in the British Antarctic Station
Cortisol followed levels followed the familiar pattern reaching highest levels as ppts awoke.
After 3 months of darkness the levels started to rise at noon
Counter Point for RS support for the importance of light (AO3)
Other research using scientific communities in the Artic found no disruption in the release of cortisol
All ppts were men…therefore cant be generalised and only 4 ppts is not representative
Individual differences (AO3)
Cycle length can vary from 13-65 hours
Individuals appear to be innately different in when their cycle reaches its peak
Duffy et al - This explains why some people wake up at different times and go to bed at different times preferably
Temperature may be more important than lighting in Circadian Rhythms (AO3)
Buhr et al suggested temp controls body clock, not light
Although light may be the trigger, the SCN transforms info about light into neural messages that set the bodies temperature
Buhr also found that these changes in the temp set the timing of cells in the body and therefore cause tissues and organs to become active or inactive
Temp changes on a 24hr scale
Temp may be more important than light
Who suggested temperature helps control the body clock, not light (AO3)
Buhr et al
Circadian Rhythm
A pattern of behaviour that occurs or reoccurs approximately every 24 hours, and which is set and reset by environmental light levels
Sleep-wake cycle
Refers to altering states of sleep and waking that are dependent on the 24-hour circadian cycle
