Biological rhythms: Infradian & Ultradian rhythms Flashcards
A01
define biological rhythm: Infradian rhythm
A type of biological rhythm that occurs less than one cycle in 24 hours
such as menstruation & seasonal affective disorder(SAD)
A01
Define biological rhythm: Ultradian rhythm
Biological rhythm that occurs more than one cycle in 24 hours
such as stages of sleep
A01
Outline Infradian rhythm-Menstrual cycle
Infradain rhythm
The menstrual cycle is an e.g of infradian rhythm, is governed by monthly changes in hormone level which regulates ovulation
The cycle refers to the time between first day of a womans period , when womb lining is shed to the day before her next period
Typical menstrual cycle is a 28 day cycle with a 6 day period of fertility, however cycles can be longer or shorter ranging between 24-35 days
during each cycle , rising levels of the hormone oestrogen causes ovary to develop an egg & release it ( Ovulation).
After ovulation, the hormone progesterone helps the womb lining to grow thicker, readying women for pregnancy
if pregnancy does not occur , egg is absorbed into body, womb lining comes away & leaves body
Progesterone-post ovulation
Oestrogen-pre ovulation
A01
Stern & McClintock study on synchronising mentrual cycles
Infradian rhythm
Stern & McClintock demonstrated how menstrual cycles may synchronise as a result of influence of pheremones
* studied 29 women with history of irregular periods
* sample of pheremones were gathered from 9 women at different stages of menstrual cycle , via cotton pad placed in their armpit
* cotton Pads worn for 9 hours ( to ensure pheromones picked up)
* the pads were treated with alcohol & told to be rubbed on upper lip of other p
* on day 1 pads from start of menstrusl cycle were applied to all 20 women, day 2 were given pad from second day, so on..
* they found women would shorten or extend their menstrual cycle to match odor donour cycle
A01
Seasonal affective disorder (SAD)
Infradian rhythm
SAD is a depressive disorder & diagnosed as mental disorder in DSM5
main symptoms of SAD are persistent low mood, lack of activity & interest in life
SAD is known as winter blues as symptoms are triggered in winter months when daylight hours become shorter
SAD is circadian rhythm as experiences of SAD may be due to disruption of sleep/wake cycle
Longer nights means that more melatonin is secreted from the pineal gland ,leading to feelings of loneliness and depression.
A01
Stages of sleep
Ultradian rhythm
example of ultradian rhythm is stages of sleep:
psychologists identified 5 distinct stages of sleep where full sleep cycle takes 90m to complete
each stage is charactiserised by different level of brain wave activity which can be monitored using EEG
* * Stage 1 & 2 the ‘sleep escalator’ refers to light sleep where p can easily be woken. at the beginning of sleep, brainwave patterns becomes slower & more rhythmic( alpha waves), becoming even slower when sleep becomes deeper (theta waves)
- stages 3 and 4 coincide with deeper and slower delta waves, difficult to wake somone up at this point
- whilst stage 5 represents REM sleep.
- The body is paralysed yet brain activity closely resembles that of awake brain . During this time , the brain produces theta waves & the eyes occasionally move around, thus rapid eye movement (REM)
- Dreams are experienced during REM sleep
A03
Stern & McClintock research has Evolutionary value
Infradian rhythm
One strength of menstrual synchrony research is that it may be explained by natural selection
* Synchronisation of menstrual cycle observed by Stern & McClintock study has evolutionary value
* For distant ancestors its advantageous for women to menstruate together & become pregnant at the same time
* In a social group , this would allow babies who lost mothers during childbearing to have access to breast milk, improving chances of survival , suggesting synchronisation is an adaptive strategy
A03
Methodological limitatiions of synchronisation
Infradian rhythm
counterpoint to McClintock & Stern
There are many factors that affect changes to menstrual cycle , including stress, changes in diet, exercise
may act as a confounding variable means that any supposed pattern of synchronisation could have been expected to occur by chance
& such research involves small samples of p, & them self reporting their own cycle
suggests that menstrual synchrony studies are flawed
A03
Individual differences-Ultradian rhythms-tucker
Ultradian rhythm-Tucker
One limitation of ultradian rhythm research is there is significant variations between people, Tucker et al found large differences between p in terms of the duration of each sleep stage , particularly stage 3 & 4
Tucker et al suggests that these differences are likely to be biologically determined
This makes it difficult to describe ‘normal sleep’ in meaningful way
