Biological rhythms Flashcards
What is a biological rhythm?
influence the way bodys system behaves
What is an endogenous pacemakers
the body’s intertnal biological clock
What are exogenous zeitgebers
external changes in the environment
What is a circadian rhythm
a biological rhythm that lasts 24 hours
What does the circadian cycle regulate
- sleep/wake cycle
- core changes in body temperature
What is the sleep wake cycle
dictates when we should be sleeping or awake
What controls the sleep wale cycle
suprachiasmatic nucleus
Outline the sleep/wake cycle
- light/ dark (exogenous zeitgbers)
are external signals that determine when we feel the need to sleep and wake up - rhythm dips/rises at certain times are strongest sleep drive is 2-4 am and 1-3pm
- sleepiness we feel during dips is less/more intense based on the amount of sleep we had
- the free running internal clock maintains a cycle of 24-25 hrs even in the absence of external cues
Out line core body temp circadian rhythm
- indicator of circadian rhythm
- lowest at 4.30 am and highest at 6pm
- sleep occurs when core temp begins to drop, temp rises during the last hours of sleep promoting alertness in the morning
- small drop in body temp occurs between 2-4pm
What was the aim of Siffre’s study
to investigate the duration of circadian rhythms particularly the sleep/wake cycle
What was the method of Siffres study?
Isolated himself from all daylight by spending 6 months in a dark cave with only artificial light. He has no clock but he had verbal contact with the outside world
What were the results of Siffres study?
His internal body clock was allowed to free run and at first it was erratic. It eventually settled into a sleep wake cycle of 25-30 hrs. He continued to fall asleep and wake up on a regular schedule. However he lost track of how long he has been in the cave. He thought was one month less that he actually did
What was the conclusion of Siffres study?
suggests that the absence of exogenous zeitgebers and circadian rhythms are roughly maintained which supports the existence of the internal body clock and that is lasts 24 hrs.
What are limitations of Siffres study?
- case study
- used artificial light
Evaluate case study as a limitation of Siffres study
- he was the sole ppt so unrepresentative snd has low population validity
- so we cant be certain his findings that exogenous zeitgebers and endogenous pacemakers work together are valid as they may apply universally
- however theres no reason to believe that Siffre isn’t a normal member of the human race and its perfectly possible that his findings indeed apply to others
Evaluate the use of artificial light as a limitation of Siffres study
- he has access to artificial light which he assumed wouldn’t affect his circadian rhythms
- However Czeizler et all managed to alter ppts circadian rhythm to 22 hours and up to 28 hrs using dim artificial light alone
- limitation of Siffres findings because it may have been the artificial light maintaining his sleep wake cycle therefore his conclusion that a free running circadian rhythm of 24 hours exists may not be valid
What are limitations of circadian rhythms
individual differences in cycle length
What are strengths of circadian rhythms
- supported by research (Siffre)
- practical applications
Evaluate supported by search as a strength of circadian rhythms
- supported by Siffres study
- his study supports the claim that humans have circadian rhythms that last 24 hours. When he isolated himself from all daylight and his internal body clock was allowed to free run it eventually settles into a sleep wake cycle of 25-30 hours
- strength of the endogenous pacemakers theory because results suggest that in the absence of exogenous zeitgebers such as natural light circadian rhythms are roughly maintained supporting the existence of an internal body clock
Evaluate practical applications as a strength of circadian rhythms
- has practical applications for shift work
- research has shown that night workers experience a period of reduced concentration at around 6am meaning mistakes and accidents ate more likely.
Research has also suggested a relationship between shift work and poor health, night workers are 3x more likely to develop heart disease which may be due to the stress of adjusting to different sleep wake patterns and lack of poor sleep quality during the day - strength because research into sleep wake cycle may have economic implications in terms of how to best manage worker productivity snd safety
Evaluate individual differences as a limitation of circadian rhythms
- claim that all humans have the same circadian rhythm has been criticised as some research has demonstrated individual differences in the sleep wake cycle
- For example Czeisler et al found that sleep wake cycles varied in some cases from 13 to 65 hours. Duffy et al found some people display natural preferences for going to bed early and rising early and others are the opposite
- limitation for some research into circadian rhythms as is suggests that not everyones sleep wake cycles are the same therefore its not possible to claim that all individuals have the same endogenous pacemakers
What is an infradian rhythm
biological rhythm with a frequency of less than one cycle in 24 hours
What are ate two infradian rhythms
Seasonal affective disorder
Menstrual cycle
What is seasonal affective disorder
depressive disorder which has a seasonal pattern of onset it is diagnosed as a mental disorder
What are symptoms of SAD
persistent low mood, lack of activity and interest in life
What triggers SAD
during winter months when daylight hours become shorter
SAD is affected by the exogenous zeitgebers light and dark
Why is SAD a circannual rhythm
subject to a yearly cycle
How can SAD also be classes as a circadian rhythm?
it may be caused due to disruptions in the sleep wake cycle due to prolonged periods of darkness in the winter
what is the menstrual cycle
-duration of more than 24hrs between 23-36 days
-its regulated by hormones and ovulation takes place halfway thru the cycle
-its is an endogenous system
What was the aim of mcclintock and sterns study into the menstrual cycle
to investigate if the menstrual cycle can be influenced by exogenous zeitgebers such as femele phermones
What was Mcclintock and sterns method
- sample of 29 women with a history of irregular periods
- sample of pheromones were collected from 9 women at different stages of the menstrual cycle by placing a cotton pad on their armpit which the wore for 8 hours
- pads were treated with alcohol and frozen to be rubbed on the upper lip of other ppts
- on day one pads from the start of the menstrual cycle were applied to all 20 women and on day two the were given pads from the second day etc
What were the results of Mcclintock and sterns study into the menstrual cycle
68% of the women experienced changes to their cycle which brought them closer to the cycle of their odour donor
What was the conclusion of Mcclintock and sterns study into the menstrual cycle
women’s menstrual cycle can be altered by communication with pheromones an exogenous zeitgeber
What are limitations of Miclintocks and Sterns study
- small sample size
- correlational
- only 68% experienced changes
- metholofical issues
Evaluate small sample size as a limitation of Mclintock and stern’s stufy
- small samle size of 29 women so has low population validity
- so the conclusion that menstrual cycle is altered by pheromones may not be valid as the same is unrepresentative to a wider population
- however theres no evidence that this is the case. its reasonable to argue that the small sample size is no sufficient reason to discount the findings
Evaluate correlational as a limitation of Mclintock and stern’s study
- evidence is only correlational
- they haven’t procent that women’s menstrual cycle can be altered by pheromones as other factors may have been involved
- however theres still clear evidence of a correlation between exposure to exogenous factors and an alteration in menstrual cycle although evidence is limited
Evaluate the fact that inly 68% of women showed a change as a limitation of Mclintock and stern’s stufy
- only 68% of the women experienced changes to their cycle which brought them closer to the cycle of their odour donor. This means that 32% didnt
- this is a limitation of their conclusions because for them to be accepted the figure must be much closer to 100%
- suggests individual differences play a role in determining the extent to which a woman’s mentrsual cycle can be altered by communication with ohermones
Evaluate methodical issues as a limitation of Mclintock and stern’s stufy
- there are many factors which effect a womans menstrual cycle including stress diet etc
- these may act as confounding variables which means the pattern of synchronisation observed may be no more that what would be expected to occur by chance
- their conclusion that a woman’s menstrual cycle can be altered by communication may be invalid
What are strengths of infradian rhythms
- supported by research (McClintock)
- practical applications
Evaluate supported by research as a strength of infradian rhythms
- supported by research
- McClintock and stern applied pheromones obtained from 9 women to 20 ppts from day 1 of their menstrual cycle. 68% of the women experienced changes in their cycle which brought them closer to the cycle of their odour donor. Suggests women’s cycle can be altered by exogenous zeitgebers
- strength because it demonstrates how pheromones play an important part in the timing of the menstrual cycle and is objective evidence that infradian rhythms exist
Evaluate practical applications as a strength of infradian rhythms
- produced effective treatment for SAD phototherapy
- this is a lightboxwhich stimulates a very strong light in the morning and evening. Its thought to-reset melatonin levels in people with SAD and relieve symptoms
- its success suggests that infradian rhythms are affected by exogenous zeitgebers such as light
What is an ultradian rhythm
a type if biological rhythm with a frequency of
more than one cycle in 24 hours
How long is each stage of sleep
90 minutes
What is stage 1 and 2 of sleep
- light sleep
person can be easily woke and brain patterns begin to slow down
What are stages 3 and 4 of sleep
- deep sleep
difficult to wake up and brain waved are even slower
What is stage 5 of sleep
- REM sleep
body is paralysed and brain activity speeds up
fast jerky movement of eyes
REM sleep is correlated with dreaming
What was the aim of Dement and Kleitmans study into ultradian rhythms
to investigate brain activity change thorough out nighttime sleep
What was the method of Dement and Kleitmans study into ultradian rhythms
7 adult males and 2 females were asked to report to the lab at bedtime where they were connected to an EEG which took measurements during sleep. pots were asked not to drink caffeinated drinks for the day before their sleep was investigated
What were the results of Dement and Kleitmans study into ultradian rhythms
they found that all ppts had periods of REM every night. Also found high incidents of dream recall when ppts were awakened during REM
What was the conclusion of Dement and Kleitmans study into ultradian rhythms
study suggests that sleep follows a typical pattern throughout the night
What is a limitation of Dement and Kleitmans study into ultradian rhythms
small sample size
What is a strength of Dement and Kleitmans study into ultradian rhythms
EEG is an objective measurement
Evaluate small sample size as a limitation of Dement and Kleitmans study into ultradian rhythms
- small sample of 9 men and 2 women meaning population validity is limited
- their conclusions that sleep follows a typical pattern throughout the night may be invalid since their sample may be unrepresentative so it may not apply to the sleep cycle of others
- however their is no evidence that this is the case. Its reasonable to argue that the small sample size isnt a sufficient reason to discount the findings
Evaluate the use of EEGs as a strength of Dement and Kleitmans study into ultradian rhythms
- EEGs provide high empiricle data
- they provide objective wvidence to show that sleep follows a typical pattern throughout night
- strength because findings provide verifiable evidence of ultradian rhytms
What is the suprachiasmatic nucleus
