bio-pscyh - biological rhythms Flashcards
explain biological rhythms?
A biological rhythm is a change in body processes or behaviour in response to cyclical changes within the environment.
E.g sleeping, body temperature (all work on 24 hours cycle)
All biological rhythms are governed by 2 things: the body’s internal biological clocks which are called endogenous pacemakers and external changes in the environment known as exogenous zeitgebers.
Circadian Rhythms are a type of biological rhythm subject to a 24 hour cycle, which regulate a number of biological processes.
e.g. sleep / wake cycle
Sunlight is an external cue to wake us up and tell us to go to sleep
2 key studies into exogenous zeitgebers?
Siffre’s cave study – Siffre spent six months in a cave, deprived of exposure to natural light and sound, but with adequate food and drink. His ‘free running’ biological clock settled down to around 25 hours and he continued to sleep and wake on a regular schedule.
This suggests that light is an important exogenous zeitgeber in terms of keeping the sleep wake cycle at 24 hours.
However the fact there is still a cycle suggests it is not completely dependent on light
This shows that endogenous pacemakers are more influential than exogenous zeitgebers in the sleep wake cycle because even when light was removed there was very little change to the sleep wake cycle. However it was an hour longer which suggests that exogenous zeitgebers are still required to keep the cycle at 24 hours.
Aschoff & Weber (1962) studied pps living in a bunker with only electric light and no windows. They were allowed to turn lights on and off as they wished, so the light source fitted with their body clocks. Eventually their body clocks settled into a sleep/wake cycle of 25 to 27 hours.
this further supports Siffre as Body clock settles of 25-27 hours and natural light is what keeps the cycle down to 24 hours
study to contrast cave study?
However although there was no access to natural light – they did have artificial light (assuming this would not have an effect on the free running bio rhythms).
Czeisler (1999) were able to adjust pps circadian rhythms from 22 to 28 hours using dim lighting, thus suggesting the artificial light in the caves may have acted as a confounding variable.
evaluation of exogenous zeitgebers studies?
However an issue with both of the above studies is that they utilise small sample sizes.
In particular, Siffre’s case study involved only one participant- himself.
This suggests that the findings of the study can’t be generalized to the population at large as it doesn’t account for individual differences.
Siffre’s study actually backs this evaluative point up as he noticed that as he grew older, his internal body clock ran slower, highlighting that individuals of different ages have unique circadian rhythms. This limits the external validity of the study.
practical application of research into exogenous zeitgebers?
Night workers are more likely to have poor sleep as they are trying to sleep in the day where there are exogenous zeitgebers such as light and sound therefore making it more difficult to sleep.
This combined with the circadian trough (Lowest point of cortisol and body temperature)
Economic implications – people will be less productive with less sleep which will mean there are more chances for errors which will increase costs.
economic implications of shift work?
There are also severe long term implications of shift work, Knuttson found that shift workers who had worked more than 15 years were three times more likely to develop heart disease than non-shift workers. This suggests
Where are our indigenous pacemakers are out of sync with the exogenous zeitgebers there will be a poor impact on the body’s health
Economic implication – have to use health services to treat this poor health
Economic implications – people will take more time of work due to bad health
study into phase delay?
Czeisler persuaded a company who employed workers on shifts to make forward rotating shifts (switching from a phase advance to a phase delay) and extend the amount of time between each rotation. After nine months of the new system, factory output was at an all time high, and so was workers morale
Better economic implications if we can improve output = phase delay is much easier than phase advance
However this may not work for everyone and the difficulties outlined above may also not apply to everybody
practical application into drug treatment?
Circadian rhythms co-ordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels.
This in turn can have an effect on pharmacokinetics (the action of drugs on the body and how well they are absorbed).
Research suggests there are peak times in the day or night when drugs are most likely to be effective.
This has lead to the development of guidelines to do with timing of medication such as anticancer and anti-epileptic drugs (Baraldo, 2008)
ECONOMIC IMPLICATIONS – drug therapy more effective and will spend less time in hospital
explain phase shifts?
Phase shift in your circadian rhythms means that your bedtime and wake up time will move earlier in the day (phase advance) or later in the day (phase delay).
explain the effects of jet lag in terms of biological rythms and a study to support?
Another example of how disrupting biological rhythms can affect us is jet lag.
Jet lag consists of the tiredness that occurs when travelling through different time zones, resulting in the desychronisation between exogenous pacemaker and exogenous zeitgeibers.
An interesting find within jet lag research is that travelling from east to west (England to America) is a lot easier than travelling west to east (America to England)
This is because of a phase delay, or advance.
England to America – phase delay (lengthen the day)
America to England – phase advance (shorten the day)
Recht studied the detrimental effects phase advance/ delay may incur, by studying the results of American basketball teams. He found that teams based on the west coast performed significantly worse on the east coast than teams based on the east did in the west, Recht attributed this to phase advance taking its toll on the western team.
Issues with extraneous variables when studying jet lag?
Low mood leaving holiday Screaming baby Turbulence Temperature on the plane Excitement to go on holiday
practical applications of jet lag studies?
Changing the lighting of the lights of the plane
Food in accordance to the destination – breakfast, lunch, dinner
Melatonin – when it is dark outside, melatonin is inhibited – you can buy tablets that help you to sleep
Research supports the fact that melatonin supplementation can improve sleep
what is an infradian rhythm?
A type of biological rhythm with a frequency of less than one cycle in 24 hours, (they occur less than once a day). For example, the menstrual cycle, seasonal affective disorder and hibernation.
explain the menstrual cycle?
The menstrual cycle is governed by monthly changes in estrogen levels, which regulate ovulation.
The typical cycle takes approximately 28 days.
During each cycle, rising levels o and release it (ovula tion).
After ovulation, the hormone e it (ovulation).
After ovulation, the hormone progesterone the lining of the womb to grow thicker, readying the body for pregnancy.
If pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (the menstrual flow).
Although the menstrual cycle is primarily thought of as an endogenous system, influenced by hormones evidence suggests it is also influence by exogenous factors such as light and stress.
study into menstrual cycle?
McClintok (1998) collected samples of pheromones from 9 women at different stages of their menstrual cycle via a cotton pad placed in their armpit (worn for at least 8 hours). The pads were treated with alcohol and frozen, to be rubbed on the upper lip of the other participants. On day 1, pads from the start of the menstrual cycle were applied to all 20 women, on day 2 they were all given a pad from the 2nd day of the cycle and so on. 68% of women experience changes to their cycle which brought them closer to the cycle of their ‘odour donor’.
