Biological Rhythms Flashcards
What do biological rhythms do to us
They influence the ways our bodies behaves
What are the 2 ways rhythms are regulated and governed
Endogenous pacemakers and Exogenous zeitgebers
What is an endogenous pacemaker
The body’s internal clocks that regulate biological rhythms
Example endogenous pacemaker
SCN- detects light even when eye are shut
What are exogenous zeitgebers
External factors in the environment which resets our biological clocks
What is an example of an exogenous zeitgeber
light and social cues
Who was Michel Siffre
a French cave explorer who spent 2 months in isolation in a cave without access to a clock nor a calendar or sun and only ate and drank when his body told him to
He settled into a sleep/wake cycle of 25 to 30 hours- usually just beyond the 24 hour cycle
His sleep/wake cycle had become desynchronised
What is a circadian rhythm
A biological rhythm around 24 hours
Example of a circadian rhythm
Sleep-wake cycle
What is an indradian cycle
A Biological rhythm that last longer then 24 hours
What is an Ultradian cycle
A cycle that lasts less than 24 hours
Example of an Ultradian cycle
Menstrual cycle
Example of an indradian cycle
Stages of sleep
Strengths of Circadian rhythms
Practical applications to shift work- shift work has been found to lead to desynchronisation of circadian rhythms and can lead to adverse cognitive and physiological effects
Application to Pharmacokinetics- By understanding circadian rhythms and their impact on health, it can help determine the best time to administer drug treatment
Support from cave study- Michael Siffre and what he found
Weaknesses of circadian rhythms
Issues with cave study- The Siffre study was only on an individual and the Folkard, Weaver and Aschoff studies were conducted on only a handful of people
Poor control in studies- In the cave studies, the exposure to artificial lights such as torches and phones were not controlled
What is the SCN
It is a tiny bundle of nerves cells located in the hypothalamus in each hemisphere of the brain. It is one of the primary endogenous pacemakers in mammalian species(including humans) and is influenced in maintaining circadian rhythms such as the sleep/wake cycle. Nerve fibres connected to the eye cross in an area called the optic chiasm. It receives information about light directly from this structure. This continues even when the eyes are closed, enabling the biological clock to adjust itself
How have animal studies been used to investigate the use of the SCN
Patricia DeCoursey et al. Destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural environment and observed for 80 days. The sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators.
Martin Ralph et al in another study bred mutant hamsters with a 20-hour sleep/wake cycle. When SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours
What is the role of the pineal gland and melatonin in sleep wake cycle
The SCN passes the information on day length and light that it receives to the pineal gland. This is another endogenous mechanism guiding the sleep/wake cycle. During the night, the pineal gland increases production of melatonin which has been suggested as a causal factor in seasonal affective disorder.
What is a zeitgeber
Zeitgebers means time giver. Exogenous Zeitgebers are external factors in the environment that reset our biological clocks through a process known as entrainment.
What role does light play in as an exogenous zeitgeber
it can reset the body’s main endogenous pacemaker, the SCN and thus plays as a role in maintenance of the sleep/wake cycle. Light is also an indirect influence on the key processes in the body that control such functions such as hormone secretion and blood circulation. In a study,
Scott Campbell and Patricia Murphy demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by the eyes. 15 participants were woken at various times and a light pad was shone on the back of their knees. The researchers managed to produce a deviation in the participant’s’ usual sleep/wake cycle of up to 3 hours in some cases. This suggests that light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert its influence on the brain
What is the role of social cues in the sleep wake cycle
At about 6 weeks of age the circadian rhythms in babies’ initial sleep/wake cycle begin and by about 16 weeks babies’ rhythms have been entrained by the schedules imposed by parents including adult determines mealtimes and bedtimes.
Research on jet lag suggests that adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances.
What is the limitations of research into SCN(at least 2)
One limitation of SCN research is that it may obscure other body clocks.
* Research has revealed that there are many circadian rhythms in the organs and cells in the body. These peripheral oscillators are found in organs including the lungs, pancreas and skin. They’re influenced by the SCN but also act independently.
* Francesca Damiola et al. (2000) demonstrate how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCH unaffected.
* This suggests other complexes influence the sleep/wake cycle.
❌
One limitation is that endogenous pacemakers cannot be studied in isolation.
* Total isolation studies (such as Siffre’s cave study) are extremely rare. Siffre also made use of artificial light which could have reset his biological clock every time he turned his lamp on. In everyday life, pacemakers and zeitgebers interact and it may make little sense to separate the two for the purpose of research.
* This suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research.
One limitation is that exogenous zeitgebers do not have the same effect in all environments.
* The experience of people who live in places where there is very little darkness in summer and very little light in winter tell a different story from the usual narrative. For instance, the Inuits of the Artic Circle are said to have similar sleep patters all-year round despite spending around 6 months in total darkness.
* This suggests the sleep/wake cycle is primarily controlled y endogenous pacemakers that can override environmental changes in light levels.
❌ One limitation is the evidence that challenges the role of exogenous zeitgebers.
* Laughton Miles et al (1997) recount the study of a young man, blind from birth, who had an abnormal circadian rhythm of 24.9 hours. Despite exposure to social cues, such as regular mealtimes, him sleep/wake cycle could not be adjusted. This suggests that social cues alone are not effective in resetting the biological rhythm.
❌ One limitation is research suggests that exogenous factors may play a larger role.
* Evidence suggests that people have poorer quality of sleep as they get old. This may be due to natural changes in the circadian rhythm as we age which means falling asleep earlier and broken sleep at night.
* However, studies have suggested the exogenous factors may be more responsible for the changes in sleep patterns amongst older people – Bernadette Hood et al. (2004) found that management of insomnia was improved if elderly people were generally more active and had more exposure to natural light.
What is a strength of research into the SCN
✅ One strength of the studies into the sleep/wake cycle is the use of animal studies.
* Animal studies of the sleep/wake cycle are justified because there are very similar mechanisms at work across species.
* The existence of an SCN and pineal gland in the brains of chipmunks/hamsters means that generalisations can be made to the human brain as the mammalian brain has very similar structures.
❌However, the ethics of these animals studies is a significant limitation. The animals in the DeCoursey et al study were exposed to risk when they returned to their natural habitat and most died as a result.
AO1 of the Menstrual cycle
Infradian Rhythm
Regulated by Hormones
Affected by lifestyle for example high stress can alter cycle length and diet
Ao3 of menstrual cycle
Reinberg suggested that the cycle is partly controlled by exogenous zeitgebers- a woman who spent 3 months in a cave with a small lamp for light had her cycle shorten to 25.7 days by the end of the 3 months
Russel et al also supported that exogenous zeitgebers had a control in the menstrual cycle- showed that most cycles synchronised based off odour exposure to one another
AO1 of SAD
A depressive disorder which has all the same symptoms of depression but only in the winter months
The disorder has been associated with the change of seasons(decreased amount of daylight levels)
SAD is a circannual rhythm as it is subject to a yearly cycle. Owever, it can be classed a circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and it can be attributed to prolonged periods of darkness during winter
Melatonin is implicated in the cause of SAD- during the night the Pineal Gland secretes melatonin till dawn- during winter this increases for longer which affects serotonin production
AO3 of SAD
Practical applications- one of the most effective treatments for SAD is phototherapy. This is a lightbox that stimulates very strong light in the mornings and evenings. It is thought to reset melatonin levels in people with SAD. This relieves symptoms in up to 60% of sufferers.
However, the same study recorded a placebo effect of 30% using a Sham negative ion generator. Participants were told it was another form of treatment. This casts a doubt on the chemical influence of phototherapy
AO1 of sleep
5 distinct stages- span 90 minutes
each stage can be monitored using an EEG
Stages 1 and 2 are light sleep- person can be easily be waken. At the beginning of sleep, brain waves become slower and more mytrinmic(alpha waves) and then become even slower as sleep becomes deeper(theta waves)
Stages 3 and 4 involve delta waves which are slower and have a greater amplitude then earlier wave patterns. This is known as deep sleep- difficult to wake someone
Stage 5(REM sleep)- body is paralysed but brain activity speeds up. REM- fast activity in the eyelids underneath the eye
Sleep AO3
Study by William Dement and Nathanial Kleitman monitored sleep patterns of 9 adults and PPTs in a sleep lab. Brainwave activity was recorded on an EEG and the researchers controlled the effects of caffeine and alcohol
REM activity was correlated with dreaming- brain activity varied according to how vivid dreams were and PPTs woken during dreaming reported very accurate recall of their dream
Replications have found similar findings although the samples of the original sample have been criticised
What is the McClintock Effect
- Martha McClintock observed synchronisation of menstrual cycles amongst her University friends
- She asked 135 college girls living in dorms to recall their period start dates at three times during the academic year
- Close friend groups’ periods were an average of 6.4 days apart in October decreasing to 4.6 days apart in April(later in the academic year)
- Aim: to investigate pheromones on the menstrual cycle
- Procedure: 29 women with a history of irregular periods
- 9 of the 29 provided pheromone samples from different cycle stages by wearing cotton pad under armpit for 8 hours
- On day 1, the other 20 women smelled the pads from day 1 of the other women’s cycle, on day 2 smelled pads from day 2 etc.
Conclusion: Suggests that menstrual cycles are influenced by other women’s pheromones acting as exogenous zeitgebers
