Biological Rythms Flashcards
(19 cards)
biological rhythms
biological rhythms refer to cycles in biological or psychological activity that occur over a certain amount of time
types of biological rhythms
- circadian rhythms (once every 24h)
- infradian rhythms (less than once every 24h)
- ultradian rhythms (more than once every 24 hours)
mechanisms involved in controlling biological rhythms
- endogenous pacemakers
- suprachiasmatic nucleus (SCN)
- exogenous zeitgebers
endogenous pacemakers
internal biological ‘clocks’ that allow organisms to control their internal rhythms
as a result, they set a natural ‘free-running’ rhythm in specific biological or psychological processes
suprachiasmatic nucleus (SCN)
SCN is seen as the main endogenous pacemaker in the sleep-wake cycle (circadian rhythm)
known as master clock
it is a tiny cluster of neurons located in the hypothalamus (part of limbic system) in the brain implicated in maintaining bodily rhythms
SCN can receive info about light levels and respond to this external cue to keep the rhythm in synchrony with the environment
does this by triggering the pineal gland to inhibit the production of melatonin (hormone resulting in a sleep response)
at night, the SCN triggers the pineal gland to produce melatonin to make us feel sleepy
exogenous zietgebers
literally means ‘external time-givers’
refers to any external cue that may influence or ‘entrain’ our biological rhythms (endogenous pacemakers)
alter body clocks to match the environment
eg temperature, light, noise, clock
role of endogenous pacemakers in the control of circadian rhythms
a circadian rhythm is a cycle in biological or psychological activity that occurs once every 24 hours
eg, sleep wake cycle occurs once every day
eg hormone production: melatonin (induces sleepiness) and growth hormone (build and restore the body) both peak at midnight, whereas cortisol (stress related) lowest at midnight
main endogenous pacemaker is the suprachiasmatic nucleus (SCN); tiny cluster of neurons located in the hypothalamus in the brain implicated in maintaining bodily rhythms
SCN causes the pineal gland to secrete melatonin at night which makes us feel sleepy; or inhibit the production of melatonin when it detects light (exogenous zeitgeber) to control the sleep-wake cycle
role of exogenous zeitgebers in the control of circadian rhythms
thought that CRs such as the sleep wake cycle are also influenced by exogenous zeitgebers which are ‘external time givers’ such as light, temperature, noise
these influence or ‘entrain’ our biological rhythms (endogenous pacemakers). they alter body clocks to match the environment
the SCN can respond to light (EZ), however without light the SCN still controls a rise and fall of melatonin to maintain the sleep wake cycle
suggests both endogenous and exogenous factors play role in controlling these rhythms but to different degrees
social cues eg mealtimes, exercise/work schedules act as EZs as they are usually set around the same time of the day
evaluate: circadian rhythms
- STRENGTHS
P) support for SCN as main endogenous pacemaker in sleep wake cycle from Morgan (1995)
E) studied hamsters, found if the SCN is removed, their circadian rhythms will disappear completely, but returned by transplanting SCN cells from foetal hamsters
E) ALSO hamsters given a transplanted SCN from a mutant strain of hamster with a shorter cycle of 20 hours, adopted the same activity patterns as the mutant donor. suggests the SCN regulates the circadian rhythm even when adapted
L) show cause and effect for SCN and biological rhythms, SCN is vital for circadian rhythms to function
E) BUT findings can’t be accurately extrapolated to humans
P) human evidence supports the roles of different factors in controlling circadian rhythms: Siffre (1975)
E) lived underground in cave for 6 months, with no cues from the sun (light - EZ) as to the time of day.
E) sleep-wake cycle settled into a ‘free-running’ rhythm of around 25 hours.
L) endogenous pacemakers are important in controlling the sleep-wake cycle because Siffre continued to operate a regular ‘free-running’ sleep-waking cycle on a roughly daily rhythm despite the absence of any exogenous zeitgebers
E) BUT, exogenous zeitgebers are also important eg light in entraining our body clock to stay in synchrony w outside world bc longer than 24 hours. need balance
P) Siffre’s findings supported by Aschoff and Wever (1976)
E) studied sleep-wake cycles in ppts living underground in a WWIl bunker
E) found a similar free-running cycle of around 25 hours
L) suggests that Siffre’s findings can be generalised, and that both endogenous and exogenous factors are required to maintain a 24 hourly rhythm
P) Support for role of exogenous zeitgebers in circadian rhythm control: Campbell and Murphy (1998)
E) found that if you shine light on the back of participants’ knees, this could shift their circadian rhythms.
L) implies that natural light may play a similar role in ‘entraining’ our biological clocks to keep the sleep-wake cycle in synchrony with the outside world
P) research into bodily rhythms have practical applications
E) employers can use this research to organise shift working patterns to increase worker productivity and well-being to encourage an efficient work force.
E) ongoing research into circadian rhythms is important to better understand how to help shift workers adapt to changing daily patterns (eg. less productive on night shift)
L) which can benefit workers lives as well as the economy
evaluate: circadian rhythms
- LIMITATIONS
P) biologically deterministic: research may ignore any degree of conscious control over circadian rhythms
E) Folkard et al (1985)ppts in cave w no natural light. initially exposed to a 24-hour day schedule. (unknown to them) gradually shortened the day to 22 hours by adjusting the clocks.
E) Most participants’ cycles could not keep up and reverted back to the longer rhythm BUT one participant did adapt to the 22 hour rhythm.
L) suggests that our circadian rhythms may only be controlled to a certain extent and that our endogenous mechanisms such as the SCN are the driving force behind our circadian rhythms
- extrapolation issues with animal studies eg. Morgan - mice
- case study (eg. Siffre) limited sample - can’t generalise findings
- individual differences between people - low population validity
infradian rhythms
An infradian rhythm is a cycle in biological or psychological activity that occurs less than once every 24 hours.
most obvious example is the human menstrual cycle which occurs, on average, once every 28 days.
Another human example is Seasonal Affective Disorder (SAD); a form of seasonal depression.
infradian rythms: endogenous pacemakers
Many infradian rhythms are clearly controlled endogenously (by internal biological clocks)
For example, the human menstrual cycle is governed by the pituitary gland releasing hormones which control ovulation.
infradian rythms: exogenous zeitgebers
It is thought infradian rhythms are also influenced by exogenous zeitgebers (‘external time keepers’ such as light).
It is thought that light plays a key role onset of SAD (eg less light in winter months leading to ‘seasonal depression’)
In terms of the menstrual cycle, it is thought that biochemicals called pheromones which are released in, for example, sweat, act like hormones and can influence people nearby.
evaluate infradian rhythms: STRENGTHS
P) support from Russell et al (1980)
E) took samples of sweat from one group of women (the donor group) and applied this to the upper lip of women in a second group
E) groups were kept separate and yet, the menstrual cycles of the women soon became synchronised with their individual donor. study isolated pheremones as the sole factor that could seemingly cause this synchronisation.
L) supports the idea that pheromones act as an exogenous zeitgeber in the control of the menstrual cycle
E) Nonetheless, this synchronisation was still shown to take a number of months to ‘entrain’ the endogenously controlled rhythms of each participant
evaluate infradian rhythms: LIMITATIONS
P) nomothetic approach: ignores individual differences
E) menstrual cycle varies between/within women
E) ranging from 21-35 days, and changing over a lifetime
L) findings may not be validly generalised to entire population; more idiographic approach is needed to understand the role of EZs on infradian rhythms like the menstrual cycle
ultradian rhythms
An ultradian rhythm is a cycle in biological or psychological activity that occurs more than once every 24 hours
the most obvious example is the stages of sleep which we go through in cycles, each lasting roughly 90 minutes.
Each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG.
The fact that all humans display a similar trend in the stages of sleep suggests that the rhythm is controlled by an endogenous pacemaker.
outline the stages of sleep
Stages 1 and 2:
- light sleep where the person may be easily woken
- 1 = beginning of sleep, brain wave patterns start to become slower and more rhythmic (alpha waves), 2 = becoming even slower as sleep becomes deeper (theta waves)
Stages 3 and 4
- deep sleep or Slow Wave Sleep (SWS)
- difficult to rouse someone at this point
- involve delta waves which are slower still
Stage 5
- REM sleep
- body is paralysed yet brain activity speeds up significantly in a manner that resembles being awake
- REM stands for rapid eye movement and research has suggested that REM activity during sleep is highly correlated with the experience of dreaming
evaluate ultradian rhythms: STRENGTHS
P) support that the sleep stage cycle is endogenously controlled comes from Dement and Kleitman (1957)
E) found REM activity occurred on average every 92 minutes
E) found, by waking up participants during REM sleep that this was when they were more likely to be having vivid dreams.
L) supports the timings of the sleep stage cycle, as well as similarities between people that suggest an endogenously controlled cycle
+ scientific research methods, eg EEG scans -> high internal validity/ replicability/ reliability, empirical evidence
evaluate ultradian rhythms: LIMITATIONS
P) support for role of external factors in the sleep stage cycle comes from research into alcohol, drugs and sleep: Ebrahim et al (2013)
E) found that, although alcohol may seem to aid sleep by accelerating sleep onset and sending us into a very deep sleep, it also leads to a more fragmented cycle through the sleep stages.
E) In particular, alcohol has been shown to greatly reduce the amount of time spent in REM sleep.
L) suggests the ultradian rhythm of the sleep stages can be changed a great deal by external factors (exogenous zeitgebers) which influence our endogenous pacemakers
