Biological Rhythms Flashcards
What are all biological rhythms governed by?
The bodies internal clock- endogenous pacemakers
Environmental influences- exogenous pacemakers
What type of rhythms occur for multiple times during the day?
Ultradian rhythms
What type of rhythms take longer than one day?
Infradian rhythm
What are circadian rhythms?
They last about 24 hours a day for example they are the sleep wake cycle and core temperature
What is the sleep wake cycle?
Our bodies feel awake during the day and drowsy at night and this is an effect of daylight on the body
What can daylight be known as in regards to the sleep wake cycle?
Exogenous zeitgyber
What would the sleep wake cycle be like without daylight?
It could be argued that we would not know if it was day or night- would we go to sleep at the same time?
Siffre Case Study?
A man who spent several extended periods under ground to study the effects of his biological rhythms. He was deprived of natural exposure to light and sound but had access to adequate food and drink
Siffre results?
He resurfaced in mid September 1962 but believed it was August
His bio rhythms had settled down to one that was just beyond the usual 24 hours however he did continue to fall asleep and wake on a regular schedule
Aschoff and Wever?
He convinced a group of participants to spend 4 weeks in a WW2 bunker which was deprived of natural light- all but one participant had circadian rhythms of 24-25 hours
What does the study by Aschoff and Wever suggest?
That the natural sleep wake cycle may be longer that 24 hours but it is trained by exogenous zeitgybers with a 24 hour day such as daylight hours and mealtimes
Folkard?
Studied a group of 12 people who agreed to live in dog kennels for 3 weeks retiring to bed when the clock said 11-45 and rising when it said 7-45. Over the study the researchers gradually sped up the clocks so that the 24 hour day only lasted 22 hours.
Folkard results?
Not one of the participants were able to adapt to the new regime. This suggests that circadian rhythms are rigid attitudes and hard to overcome by changes in the external environment
By how much does core body temp vary?
2 degrees
When is core body at lowest?
4 in morning - 36 degrees
When does core body temp peak?
Around 6 in evening - 38
What does body temp correlate to?
Better cognitive performance- when we are warmer we are thought to perform to a higher standard
Folkard et al- body temp?
Demonstrated how children who have stories read to them at 3pm showed superior recall and comprehension after a week compared to children who heard the same story at 9am
Gupta?
Found improved performance on an IQ test when participants were assessed at 7pm as opposed to 2pm and 9am
What is a practical application of circadian rhythms? E
We now have a better understanding of the adverse consequences that occur as a result of their disruption. Night workers engaged in shift work experience a reduced level of concentration at 6AM ( the circadian trough) meaning that accidents are more likely to happen
Bovin? E
Research has suggested a link between shift work and poor health as shift workers are 3 times more likely to develop heart disease due to the stress they experience when adjusting to new sleeping patterns and lack of poor quality sleep during day
Knutsson 2003? E
Research may have economic implications in terms of how best to manage worker productivity
What do circadian rhythms affect within the body?
Heart rate, digestion and hormone levels
How has research influenced pharmocokinetics? E
Research has shown that there are peak times within the day or night when drugs are likely to be most effective- this has led to the guidelines to do with the timing of drugs for a whole range of medications including anti-cancer and anti-epileptic drugs
Why are case studies that provide research into CR limited? E
Tend to involve small groups of participants or single individuals- these people may not be representative of a whole population and limits the extent that meaningful generalisations can be made
Limitation of Siffre study? E
Siffre observed at the age of 60 that his internal clock was slower than when he was a younger man- even though the same man was involved there are factors that vary and impact on bio clocks which may prevent general conclusions being drawn
How was there a poor control of Siffre study? E
The participants still had access to artificial light which remained on until they went to bed
Czeisler et al? E
Participants were able to adjust circadian rhythm to between 22-28 hours
Influence of individual differences in sleep wake studies? E
Individual cycles may vary in some cases from 30-65 hours - some people display a natural preference for example going to bed early or rising early while some people prefer the opposite- there are also age difference in sleep wake cycles (teenagers)
Case study of Monkseaton high school?
Tried to alter body clocks by starting school at 10
What is an example of an Infradian rhythm?
The menstrual cycle - governed by monthly changes in hormone levels which regulate ovulation
Time = first day of cycle and first day of next cycle
Menstrual cycle- how long does it last?
28 days
Purpose of menstrual cycle?
Hormone oestrogen causes the release of an egg
Pro-oestrogen lines the uterus
Stern and McClintock?
Demonstrated how the menstrual cycle may synchronise due to female pheromones- 29 women with history of irregular periods. A sample of pheromones from 3 women at different stages in cycle were taken via cotton pad under arm pit- pads frozen and treated with alcohol and rubbed on upper lip of other women. Day one pheromones from first day etc
McClintock results?
68% of women experienced changes to their cycle which brought them closer to the cycle of the woman who provided the pheromones
What is SAD?
Often referred to as winter blues as symptoms as triggered during winter months when daylight hours become shorter- symptoms include- low mood alongside general lack of interest in life
What type of rhythm is SAD?
A type of infradian rhythm- circannual rhythm as it is subject to a yearly cycle
How can SAD be classified as a circadian rhythm?
Relates to disruption of the sleep wake cycle due to prolonged hours of darkness
What hormone is important in the SAD?
Melotonin
How does melotonin influence SAD?
During the night the penal gland secretes melatonin until there is an increase in serotonin- during winter the lack of daylight means that this secretion process takes longer- influences production of serotonin which is linked to the onset of depressive symptoms
Example of ultradian rhythm?
Sleep stages- distinct stages that last for approx 90 mins- each characterised by a different level of brain activity which can be monitored using an EEG
Stage 1 and 2 of sleep cycle?
1- brain patterns become slower and more rhythmic (alpha waves)
2- become even slower and deeper ( theta waves)
Stages 3/4 of sleep cycle?
Involve delta waves which are slower still and have a greater amplitude than earlier patterns- this is deep sleep and it is difficult to rouse someone at this point
Stage 5 sleep cycle?
The body is paralysed yet brain activity speeds up significantly
Rapid eye movement activity during sleep is highly correlated with dreaming
Why is it thought that the menstrual cycle could have been of evolutionary value? E
It may have been advantageous for our ancestors to menstruate together and therefore fall pregnant around the same time, this would mean that new born babies could be cared for together increasing the chance of survival
Schank? E
Argues that if there were too many females menstruating at the same time there would be competition for the highest quality male so avoidance of synchrony would be the most adaptive strategy
Confounding variables in menstrual studies? E
Stress, changes in diet and exercise- therefore any support pattern of synchronisation is no more than would have been expected to occur by chance
Methodological issue with menstrual studies?E
Small sample of women would have been used- issues with generalisation- relies on participants self-supporting the onset of their own cycle
Cultural issues with menstrual cycles?E
Other cities have failed to find any evidence of menstrual symphony in all female samples
Dement and Kleitman evidence for sleep cycles? E
Monitored sleep patterns in 9 participants in a sleep lab, brainwave activity was recorded on an EEG and the researcher controlled levels of caffeine and alcohol- REM activity was highly correlated with dreaming, brain activity varied according to how vivid dreams were
Evaluation of Dement and Kleitman study? E
Replications have noted similar findings however the small sample size was initially criticised by some- REM is an important component of the Ultradian sleep cycle
Importance of animal studies in role of pheromones? E
Knowledge is derived from animals for example how sea urchins release pheromones so that those in the colony will adjust their sex cells simultaneously - evidence for the effect of human behaviour remains speculative and inconclusive
Practical application of SAD? E
Led to the development of phototherapy- a light box that stimulates strong light in the morning and afternoon- it is thought to reset melatonin level
Effectiveness of phototherapy? E
Reduces symptoms by 60%
Placebo effect= 30%- casts doubt on influence
What does SCN stand for?
Suprachiasmatic nucleus
What is the SCN?
Endogenous pacemaker- A tiny bundle of cells located in the hypothalamus in each hemisphere of the brain- influential in maintaining security in sleep wake cycle
What information does SCN receive?
Information about light via the optic chasm - this continues even when our eyes are closed enabling the bio clock to adjust to changing patterns of light
How do animal studies support SCN importance?
The SCN connection of 3000 chipmunks and then returned them to their natural habitat for 80 days- sleep wake cycle had disappeared and most of them had been killed by predators
Ralph hamster study?
Bred mutant hamsters to have a sleep wake cycle of 20 hours- when SCN cells were transported from fetal tissue to normal hamsters the cycles of the normal group defaulted to 20 hours
Role of pineal gland?
Receives information about light from SCN and during the night the gland increases production of melatonin - which induces sleep
Define the process entrainment?
Environmental triggers reset our body clocks
What is body main zeitgyber?
Light- important in sleep wake cycle and hormone secretion
Campbell and Murphy?
Light may be detected by skin receptors even if not sought by eyes for example light shone on someone’s back of knee woke 15 participants
Role of social cues in rhythms?
Babies develop circadian R at 6 weeks, by 16 weeks most are entrained- schedules imposed by parents can be key to influencing a baby for example if travelling through time zones maintain same meal times to beat jet lag
