Environmental - Biological Rhythms Flashcards
Circadian Rhythms (Background)
- Happen over a period of ~24hrs
- Some circadian rhythms play a role in changes in our state of consciousness
- Examples include the sleep-wake cycle, homeostasis, blood pressure, blood sugar, body temperature
Endogenous Pacemakers (Background)
Internal mechanisms that control natural rhythms e.g. the SCN
Exogenous zeitgebers (Background)
External factors that control natural rhythms e.g. light levels, time, surrounding environment
Sleep-wake cycle (Background)
Endogenous pacemaker - SCN, a part of the hypothalamus
Exogenous zeitgeber - light levels and time e.g light levels signal to the SCN to control levels of melatonin production
Phase shifts (Background)
- When your sleep wake cycle entrains itself to match a new circadian rhythm
- Phase delay: going around the world clockwise (+hrs, preferred direction)
- Phase advance: going around the world anticlockwise (-hrs)
Siffre - Cave Study (Background)
Stay 1: 61 days in the Southern Alps (1962) - he resurfaced on 17th September believing it to be August 20th, showing his circadian rhythm to be around 26hrs
Stay 2: 6 months in a cave in Texas - his natural circadian rhythm settled down to just over 24hrs but with some dramatic variations
Stay 3: done in 1999 to study the effects of ageing on his circadian rhythms - found that his body clock ticked more slowly compared to when he was a young man, sometimes stretching his circadian rhythms to 48hrs
This shows that whilst the natural circadian rhythm of humans is ~24hrs, light is important to reset the natural rhythm
Menaker et al. + Ralph et al. - Hamster studies (Background)
Menaker et al.
- Bred a strain of hamsters to have a circadian rhythm of 20 rather than 24hrs
- SCN neurons from these abnormal hamsters were then transplanted into the brains of normal hamsters
- Circadian rhythms switched - mutated hamsters had 24hr circadian rhythm and vice versa
- This shows the importance of the SCN in regulating circadian rhythms
Ralph et al.
- Also manipulated hamsters to have a 20hr circadian rhythm programmed by the SCN
- They transplanted SCNs (20 hrs) into normal hamsters and their circadian rhythms changed to 20 hrs
- CONCURRENT VALIDITY - backs up the claim from the prior studies that the SCN plays a key role in controlling circadian rhythms
Campbell and Murphy - Office study (Background)
- 15 volunteers slept in a lab
- Ps were woken up at different times and a light pad was shone on the back of their knees
- Their circadian rhythms fluctuated by up to 3hrs from their normal 24h cycle
- Suggests we do not rely solely on light entering the eyes in regards to circadian rhythm changes
Klein et al. - Blind man case study (Background)
Blind man had a circadian rhythm of 24.5hrs and his circadian rhythm eventually got out of sync
- Time cues did not help him entrain to the normal 24h day
- He had to take stimulates and sedatives to regulate his sleep-wake cycle to fit the normal day
- Shows that light is an important exogenous zeitgeber controlling the sleep-wake cycle
Czeisler et al. - Aims + Hypotheses
- Researchers aimed to take advantage of the properties of the circadian rhythms that individuals share in common
- Theorised that work schedules that rotate should do so by successive phase delays
- Also theorised that the interval between phase shifts should be great as it is practical
Czeisler et al. - Method
- Field experiment using matched groups design with comparable jobs
- IVs - what shift they were on
- DV - responses to questionnaire on health
- Questionnaires used to gather data in relation to measures of worker satisfaction, worker health, personnel turnover, and productivity before and after the introduction of new shift work schedules
Czeisler et al. - Sample
- 85 male rotating shift workers
- Control group of 69 male non-rotating and swing shift workers with comparable jobs
- All ps selected from the Great Salt Lake Minerals and Chemicals corporation in Utah
- Response rate was 84%
Czeisler et al. - Procedure
- Each worker (p) was given health-index questionnaires before new shifts were introduced
- Shift workers on rotation were divided into 2 groups where 33 workers continued rotating weekly and 52 workers rotated once every 21 days in phase delay
- Before implementation of the schedule, all workers and managers attended a presentation about the properties of the circadian sleep-wake cycle
- After 3 months the same questionnaires were redistributed
- Personnel turnover and plant productivity were analysed 9 months after the introduction of the new schedules
Czeisler et al. - Results
- 81% of workers
- Shift workers preferred the phase delay shift, with an increase on the schedule satisfaction index and improvements in health index
- Shift worker’s complaints about schedules dropped from 90% to 20%
- Less staff turnover happened as a result of the new changes
Czeisler et al. - Conclusions
- Rotating shifts in the phase delay direction are most compatible with natural circadian rhythms
- Application of circadian principles to the design of schedules improve shift workers’ satisfaction, health indices and productivity
