circadian rhythms Flashcards
What are circadian rhythm’s
A pattern of behaviour that occurs or recurs approximately every 24 hours, and which is set and reset by environmental light levels.
The nature of circadian rhythms
Our circadian rhythms are driven by our body clocks, found in all cells of the body and synchronised by the master circadian pacemaker, the SCN, found in the hypothalamus.
This pacemaker must constantly be reset so that our bodies are in synchrony with the outside world.
Light provides the primary input to the system, setting the body clock to the correct time in a process termed photo entrainment.
three examples of circadian rhythms
sleep-wake cycle
core body temp
hormone production
Sleep-wake cycle
Dictates when humans and animals should be asleep and awake.
Lightprimary input to this system, acting as the external cue for sleeping or waking. Light is first detected by the eye, which then sends messages concerning the level of brightness to the SCN.
The SCN then uses this information to coordinate the activity of the entire circadian system.
Sleeping and wakefulness are not determined by the circadian rhythm alone, but also by homoeostasis.When an individual has been awake for a long time, homeostasis tells the body that there is a need for sleep because of energy consumption. This homeostatic drive for sleep increases throughout the day, reaching its maximum in the late evening, when most people fall asleep.
Core body temp
Human body temperature is at its lowest in the early hours of the morning (36C at 4:30 am) and at its highest in the early evening (38C at 6 pm).
Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning.
Hormone production
For example, the production and release of melatonin from the pineal gland in the brain follows a circadian rhythm, with peak levels occurring during the hours of darkness. By activating chemical receptors in the brain, melatonin encourages feelings of sleep. When it is dark, more melatonin is produced, and when it is light again, the production of melatonin drops and the person wakes.
Case study
Siffre (1973) conducted research in which he spent two months in a cave deprived of light and sound.
When Siffre emerged from the cave he found that his circadian rhythm remained between 24-25 hours
He also stated that he had kept to his usual habits i.e. going to sleep and waking at the usual times
Desynchronisation of circadian rhythms
Shift work and jet lag have been found to lead to the desynchronisation of circadian rhythms and can lead to adverse cognitive and physiological effects e.g.
memory lapses
poor concentration
issues with fertility
increased risk of cancer, heart disease and diabetes
AO3: circadian rhytms
Str: research
Lim: research
lim: indiv diffs
circadian rhythms str: research
Subsequent research (after Siffre’s original study) supports the idea that the sleep-wake cycle has a duration of just over 24 hours and that any interference with this cycle is likely to be detrimental to functioning
Folkard et al. (1980) implemented a 22-hour sleep-wake cycle and found that participants experienced problems with recall in their short-term memory
This gives the theory of the sleep-wake cycle good validity
Research which has found that desynchronisation has deleterious effects on people has been highly useful in practice
Employers are advised not to allocate night shift work to employees for long periods of time to minimise the negative consequence
circadian rhythms lim: research
Siffre’s study included one participant: himself
This is a limitation as it means that:
-the results cannot be generalised to anyone else
-he may have lost objectivity e.g. by misinterpreting his sleep-wake cycle or using confirmation bias in his reporting of the results
-there is no one else to check his findings
circadian rhythms lim: individual diffs
Duffy et al. (2001) found that ‘morning people’ prefer to rise and go to bed early (about 6 am and 10 pm)
Whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am).
This demonstrates that there may be innate individual differences in circadian rhythms
Which suggests that researchers should focus on these differences during investigations.
