biological rhythms
circadian rhythms
approximately 24 hour duration
regulated by internal body clock (endogenous pacemaker) and external cues ( exogenous zeitgebers)
sleep/wake cycle
2) pineal gland: receives info from SCN to release melatonin which induces sleep
3) adrenal gland: releases cortisol which induces wakefulness
1) suprachiasmatic nucleus (SCN) an example of endogenous pacemaker, found in hypothalamus which is connected to the visual cortex. is a tiny bundle of fibres that receives information about light- exogenous
4) exogenous Zeitgebers; including light do impact and reset the exogenous zeitgeber as light receptors on the retina send signals to the SCN
evaluation
supporting evidence from siffre who spent long periods underground to study his effects on biological rhythms. spent 2 months in a cave in the Alps and in the absence of natural light he length of the sleep/wake cycle was just beyond 24 hours. suggests endogenous pacemakers are more important than maintaining circadian rhythms than exogenous zeitgebers
limitation- siffres study is a case study so cannot be generalised to general population
entrainment
process of aligning the internal body clock (endogenous pacemaker) to external cues (exogenous zeitgeber). this is important in regulating the body's biological rhythms
infradian
ultradian
'ultra short'- less than 24 hours
sleep stages
evaluation
strength- evidence support. monitored sleep patterns of 9 ptpts . found by EEG that REM activity was highly correlated with dreaming. also woke up ptpts at different stages of sleep and found that ptpts frequently described dreams in the REM cycle but not in the nREM cycle.
there are 5 stages that make up a typical nights sleep. each complete cycle takes from 90 to 110 minutes and a full nights sleep has 4 or 5 cycles
length of time in each stage varies according to how far through the nights sleep the sleeper is, their age and how tired they are
stage 1 and stage 2
relaxed state, easily woken, heart rate slows, temp drops. little eye movement and muscles become more relaxed
stages 3 and 4
growth hormone produced, not easily woken. almost no eye movement, muscles completely relaxed
REM sleep
brain and eyes active but body paralysed. stage of sleep where we dream and enables brain recovery/restoration
move from stages 1,2,3,4 and back to stage 2 then experience REM sleep. periods of REM sleep get longer as the night progresses
duration greater than 24 hours
menstrual cycle
typical cycle takes approximately 28 days to complete
FSH
folicle stimulating hormone, leads to the production of oestrogen and progesterone which thickens and maintains uterus lining
LH
lutenizing hormone, triggers ovulation
governed by monthly changes in hormones levels which regulate ovulation
during each cycle rising levels if oestrogen cause the ovary to develop an egg and release it (ovulation). after ovulation, the hormone progesterone helps the womb lining to grow thicker, readying the body for pregnancy. if pregnancy does not occur the egg is absorbed into the body, the womb lining sheds (menstrual flow)
evaluation
evidence to support. studied 29 women with history of irregular periods. found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor'.
evaluation of infradian&ultradian
limitation- research is flawed as used EEGs as method of brain scanning, which have poor spatial resolution so hard to pinpoint location of dreaming in the brain. also used small sample which isn't representative and cannot be generalised. so, lacks validity
the effect of endogenous pacemakers and exogenous zeitgebers on the sleep wake cycle
endogenous pacemakers
practical application- understanding of infradian rhythms has led to effective treatments of seasonal affective disorder (SAD)- a disorder characterised by persistent low mood during winter months. phototherapy is a strong Lightbox that stimulates a strong light in the morning and evening. acts to reset melatonin levels for people with SAD. means understanding can lead to positive influence of peoples lives
exogenous Zeitgebers
anything whose origins are within the organism
allows us to keep pace with changing cycles in the environment
SCN is most important pacemaker, which lies with the hypothalamus and acts as a 'master clock' controlling the sleep wake cycle
strength- supporting evidence for importance of endogenous pacemakers in circadian rhythms. bred hamsters to have circadian rhythms of 20hrs long then transplanted these into brains of normal hamsters and found these took on the abnormal rhythms. problem with generalisability as research done on animals. emphasises importance of SCN in understanding endogenous pacemakers on the circadian rhythms
light
how does light affect the circadian rhythm?
2) sends a signal to the SCN
social cues
resets the body main endogenous control systems.
suppresses the release of melatonin from the pineal gland, influencing sleep/wake cycle
suggests sleep/wake cycle not only influenced by endogenous pacemakers
3) the SCN sends a signal to the pineal gland
1) high levels of light is picked up by receptors in the eye
4) the pineal gland will stop releasing melatonin due to the high levels of light
make us less alert once we have finished our evening meal
research suggests that adapting to local eating and sleeping times before travelling to a different time zone can prevent jet lag, suggesting that exogenous zeitgebers can influence the sleep/wake cycle
strength- supporting research, woke up 15 ptpts and shone a light on the back of the knee. produced a deviation of the usual sleep/wake cycle up to 3 hours for the ptpts. suggests light is a powerful exogenous zeitgeber that does not even need to be the eyes to have an influence on the circadian rhythms
evaluation
limitation- research flawed as usually uses small number of ptpts or animal studies to make conclusions therefore limits generalisation