Circadian Rhythms

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