Biological rhythms Flashcards
a biological rhythm is
a distinct pattern of change in body activity that conforms to cyclical time periods
rhythms can be affected by internal body clocks or external environment changes
circadian rhythm
a type of biological rhythm that has 24 hour cycle, which is regulated by a number of body processes
eg. sleep/wake cycle, core body temperature
these cycles can also be affected by factors eg age
sleep wake cycle
daylight = exogenous zeitgeber
most humans feel tired during night but alert during the day
presence of daylight keeps this rhythm in check
research has investigated how this circadian rhythm would cope without this important EZ
Siffre’s cave study
siffre spent several periods in caves without natural daylight to see what effect this had on his natural sleep/wake cycle
on 1 occasion he was deprived of daylight for 2 months
he found that without presence of daylight his 24hr sleep/wake cycle ran just under 25 hours
core body temperature
body temp varies by 2degrees
lowest at 4am (36) highest at 6pm (38)
evidence suggests that body temp affects cognitive abilities eg. the warmer we are internally, the better our cognitive performance
Gupta (1991) found that children’s IQ was better at 7pm compared to 2pm or 9am
strength of circadian rhythms - useful to help with knowledge of shift work
P: research useful to help with knowledge of shift work
E: highlighted consequence of shift work eg. disruption to cycle - desynchronisation. night workers experience dip in concentration at 6am. so more likely to make mistakes + nurses could put patient’s lifes at risk. link between shift work + poor health - long term night shifts 3x more likely to develop CHD + stress due to cycle disruption
C: they have developed night shift rotations, shorter night shifts, + breaks for them. less people need treatment from NHS
strength for circadian rhythms - siffre
P: support for Siffre’s research into circadian rhythms
E: in similar study, Ps stayed in underground bunker for 4 weeks. all but 1 showed change in sleep/wake cycle - extended to 25hours
C: findings have consistency so are reliable
limitation of circadian rhythms - case study
P: use of case studies eg. Siffre’s cave study
E: case study is an in depth investigation into a person/small group. the sample used one middle aged French man (Siffre)
C: small sample - unrepresentative so can’t generalise findings. doesn’t tell us about sleep/wake cycle in everyone else
limitation of circadian rhythms - contradictory research
P: contradictory research suggests that sleep/wake cycle is 24hrs for everyone
E: research suggested that sleep/wake cycle can vary from 13-65 hrs in some cases. further research suggests that age plays a major role in S/W cycle with teenagers cycle starting 2 hours after adults.
C: inconsistencies mean findings lack validity so it’s unreliable
infradian rhythms =
type of biological rhythm that has a frequency of less than 1 cycle every 24 hours eg. monthly/yearly
menstrual cycle/seasonal affective disorder
menstrual cycle
cycle governed by change in hormones - oestrogen + progesterone - endogenous pacemakers
cycle lasts for 28 days
cycle thought to be regulated by exogenous factors such as cycle of other women - exogenous zeitgeber
Martha McClintock’s study
used 29 women with irregular periods
samples of pheromones taken from 9 women (odour donors) - placed cotton pad in armpit
samples treated with alcohol + then wiped across top lip of Ps
68% experienced changes in cycle which brought them closer to cycle of odour donor
seasonal affective disorder
depressive disorder that has seasonal pattern of onset
symptoms - persistent low mood/lack of interest in activity. symptoms triggered in winter months
thought that hormone melatonin is responsible. increased release of melatonin in winter has knock on effect on serotonin
strength of infradian rhythms - treatments for SAD
P: understanding of infradian rhythms useful for development of treatments for SAD
E: ‘light box’ effective form of treatment for SAD. box stimulates very strong light in morning + evening. aim to reset levels of melatonin - studies reported that 60% of sufferers found reduction in symptoms
C: better quality pf life. benefits economy as people wouldn’t have to take time off work + can spend disposable income
limitation for research into infradian rhythms - sample size
P: sample sizes were small
E: in McClintock’s study, 29 women made up the study. so unrepresentative
C: can’t generalise findings so doesn’t tell us about infradian rhythms in real life
ultradian rhythms
type of biological rhythm that has a frequency of more than 1 cycle in 24 hours.
eg. stages of sleep. cycle occurs several times per night
stages of sleep
psychologists have identified 5 stages of sleep which span for 90 mins
90 min cycle occurs several times a night
each stage can be identified by brain waves that they produce - can be recorded by using EEGs
stage 1 + 2 of sleep
known as light sleep - person can be easily woken
start as alpha waves which are lower but then develop into theta waves which are deeper
stage 3 + 4 of sleep
deep sleep
waves change to delta waves which are slower than waves produced in stage 1 + 2
stage 5 of sleep
Rapid Eye Movement (REM) sleep
body is paralysed but brain activity is similar to that produced when we are awake.
this is the stage where dreaming happens
strength of ultradian rhythm
P: studying stages of sleep is scientific
E: EEG used to study stages of sleep. results have consistently reported the same findings eg. REM sleep is correlated with dreaming
C: allows C+E relationship between brain nerve activity and the stages of sleep correlated with brain nerve activity. scientific methods allow standardised procedures to be used so it can be replicated so it’s reliable
limitation of research into ultradian rhythms
P: there is a lot of variation between people when it comes to sleep
E: Tucker (2007) found that when analysing the stages of sleep there was a lot of differences between people eg. how long each stage lasted for
C: it affects our understanding of what normal sleep patterns look like. so, we can’t determine what abnormal sleep patterns look like.
biological rhythms are influenced by 2 factors:
- internal body clocks (endogenous pacemaker)
- external cues within environment (exogenous zeitgebers)
endogenous pacemakers =
internal body clocks that regulate many of our biological rhythms eg. suprachiasmatic nucleus (SCN) on sleep/wake cycle
the suprachiasmatic nucleus
tiny bundle of nerve cells found in hypothalamus in each hemisphere
primary endogenous pacemaker - helps maintain our circadian rhythms
light and the suprachiasmatic nucleus
when it’s light the SCN which lies in visual area of cerebral cortex detects this
this processing occurs when our eyes are shut, which helps us to adjust to changing patterns of daylight whilst we are asleep
SCN - pineal gland and melatonin
SCN passes info on day length + light to pineal gland - lies beneath hypothalamus
during night, pineal gland increases production of melatonin (helps bring on sleep)
when we wake, pineal gland reduces production of melatonin which helps us stay awake
exogenous zeitgeber
external cues that may affect our biological rhythms such as influence of light on our sleep/wake cycle
EZs - light
light is a key zeitgeber as it activates SCN which is involved in S/W cycle
in 1 study, they shone a torch on back of people’s knees whilst they slept - researchers managed to disrupt some cycles by up to 3 hours
shows light doesn’t just have to be detected by eyes
EZ - social cues
babies S/W cycles are random - begin to form at 6 weeks + become regular at 16 weeks
parents use social cues in form of schedules such as feeding + nap times to regulate babies cycle
babies should sleep in the dark to encourage SCN functioning
strength of EZs - useful
P: research into effect of EZs is useful
E: studies have shown negative effects of increasing usage of electronic media especially late at night. blue light leads to suppression of melatonin which is essential for sleep. this causes disruption to S/W cycle causing sleep to be irregular, shortened + delayed
C: raised our awareness on how poor sleep hygiene negatively effects health. so, by getting people into good sleep hygiene it places less stress on the body which in turn, gets rid of negative implications on economy
strength of EP - supportive research
P: supportive research into importance of EPs (decoursey et al)
E: research had destroyed the SCN connections in brain of 30 chipmunks. they then retuned them to their natural habitats + observed for 80 days. found that S/W cycle had disappeared - large number of chipmunks killed by predators due to this.
C: shows that SCN is vital in S/W cycle. so, it expresses importance of EPs in S/W cycle.
however - unable to generalise findings of chipmunks to humans due to them being a completely different species
limitation of EZs - contradictory evidence
P: contradictory evidence questions real influence of EZs
E: Miles et al (1977) studied a young blind man from birth - circadian rhythm of 24.9 hours. despite exposure to social cues, his S/W cycle couldn’t be adjusted. he had to take sedatives to help him sleep to keep up with 24 hour world.
C: shows that there may be occasions where EZs have little influence over our circadian rhythms
