Biological Rhythms

Question 1

Circadian rhythms

Answer 1

• Often referred to as our body clock.
• Last approx 24 hours
• Means about a day.
• Most common and studied of biological rhythms.
• Sleep wake cycle - has one period of sleep and one period of waking every 24 hours. Body temp has one peak and one trough every 24 hours.
• Many hormones such as cortisol follow same circadian pattern.

Question 2

Nature of circadian rhythms

Answer 2

• Rhythms driven by body clock, found in all cells of the body.
• Rhythm synchronised by master circadian pacemaker - SCN found hypothalamus in centre of the brain.
• SCN must be constantly reset so that our bodies are in synchrony with outside world.
• Regulated by light from our environment in a process called photoentrainment.
• In mammals, light sensitive cells within the eye act as brightness dectectors, sending messages about environmental light levels direct to SCN.
• SCN coordinates activity of entire circadian system.

Question 3

Sleep wake cycle

Answer 3

• Circadian rhythm dictates when we should sleep but when we also should be awake.
• Light and darkness are signals that determine when we feel need to sleep and wake.
• Before bed - body temp drops, bloody pressure drops, cognitive performance declines and tiredness increases.
• Before dawn - metabolism geared up to anticipate increased activity when we wake.
• Rhythm dips and rises during day - strongest dips between 2-4 am and 1-3 pm.
• System keep us awake as long as there is daylight and prompts us to sleep when dark. When cues are eliminated rhythms become free running.
• Run only to 24 hour day - require daily adjustment to light dark cycle by external cue to reset to environment.
• Fact rhythms persist even under constant environmental conditions - must be biological clock - jet lag and night shift can unbalance this clock.

Question 4

Michael Siffre

Answer 4

• 23 year old French cave explorer.
• Lived in glacial cave for 2 months - 120 metres below surface.
• No daylight, no clock, no radio.
• Wrote and slept when he felt the need to.
• Only thing influencing him was internal body clock.
• When resurfaced on 17th September, he thought it was 20th August.
• Mind lost track of time. Body had not lost track of circadian rhythms as it was settled into a rhythm of just over 24 hours.
• This shows that circadian rhythms persist despite isolation from natural light - demonstrates existence of endogenous clock or body clock.
• However - shows external cues are important as the clock was not always accurate on its own - it varied.

Question 5

Folkard et al

Answer 5

• Conducted an experiment to see if external cues could be used to override the internal clock. - group of 12 people lived in a cave for 3 weeks. Isolated from natural light and other time cues.
• Volunteers agreed to go to bed when clock indicated 11.45pm and get up when it indicated 7.45am
• Clock ran normally at start but they gradually quickened the clock until is was indicating the passing of 24 hours with only 22 hours.
• At start rhythm matched clock but as it was quickened none could adjust.
• Suggests that there is a strong free running circadian rhythm and this cannot be easily overridden.

Question 6

Silver

Answer 6

• Removed SCN from hamsters and they lost their daily sleep wake pattern - still did normal activities bit at erratic times. - Showed SCN linked to hamsters daily rhythms.
• Although well controlled - does not prove that SCN is body clock. By removing SCN researchers may also have damaged other areas nearby and this could have damaged activity.
• Silver carried out a second study - implanted foetal hamster SCN cells into adults missing SCN. - Over next few days they regained rhythm demonstrating the link.

Question 7

Core body temperature

Answer 7

• One of the best indicators of the circadian rhythm.
• Core temp varies by 2 degrees during the course of the day with its lowest point at 4 in the morning and peaking around 6 in the evening.
• Evidence suggests that body temp may have an effect on our mental abilities - warmer we are the better our cognitive performance.
• Folkard found that children who had stories read to them at 3pm showed superior recall and comprehension after a week compared to children who heard same stories at 9am. Shows that circadian rhythms affect mental abilities.

Question 8

Evaluation of Circadian Rhythms - Research Support

Answer 8

• Wealth of supporting research.
• Hughes tested circadian hormone release in 4 p stationed at British Antarctic Station. End of Antarctic summer cortisol levels followed a familiar pattern - high when p awoke and low at bedtime.
• However, after 3 months of total darkness pattern changed with men having highest peak at noon rather than when they awoke.
• Strength - suggests extreme of daylight found in Polar Regions present considerable change for physiological processes that depend on circadian rhythms. Supports influence of environmental cues on internal biological clock. Also demonstrated in temporal isolation studies.

Question 9

However - research support

Answer 9

• Circadian rhythm studies tend to involve small groups of p or studies of single individuals.
• People involved may not represent wider population.
• Weakness - case studies and small samples limits extent generalisation can be made.

Question 10

Evaluation of Circadian rhythms - supporting animal research

Answer 10

• wealth of animal research
• Silver study using hamsters well controlled.
• Empirical study clearly showed role of SCN in maintaining cycle.
• Strength - shows biological/internal controls are essential in maintaining a regular pattern of activity.

Question 11

However - animal studies

Answer 11

• Hamsters are nocturnal so not necessarily representative of all mammals.
• Weakness - limits generalisability.

Question 12

Evaluation of circadian rhythms - practical applications

Answer 12

• knowledge of circadian rhythms has given researchers much better understanding of adverse consequences that can occur with their distruption.
• Night workers who shift work experience period of reduced concentration at around 6 am - circadian trough.
• Mistakes and accidents more likely. Relationship between ill health and shift work also been suggested - due to stress of adjusting do different sleep patterns and lack of good quality sleep during the day.
• Strength - research into sleep wake cycle have economic implications in terms of how best to manage worker productivity.

Question 13

Furthermore - practical applications

Answer 13

• Understanding of circadian rhythms and impact on health can help determine best time to administer drug treatments.
• Means that there are peak times for administration and dosage of variety of drugs that treat range of disorders such as cancer, epilepsy and a range of respiratory issues.
• Risk of heart attack is greatest in early morning so drugs can be taken at night, effect not released until it will be most effective.
• Strength - led to development of guidelines for whole range of medications in order to increase effiacy.

Question 14

Menstrual Cycle

Answer 14

• Rhythms have period greater than 24 hours less than a yer.
• Lasts approx 28 days.
• Driven by fluctuating hormone levels and purpose of cycle is to regulate ovulation.
• Pituitary gland releases follicle stimulating hormone and lutenizing hormone which stimulates one follicle in one ovary to ripen an egg and release oestrogen.
• When egg has ripened, ruptured follicle starts to secrete progesterone, causing lining of womb to thicken.
• If no pregnancy two weeks after ovulation level of progesterone falls and lining of womb is shed and leaves body.

Question 15

Research on Menstrual Cylce

Answer 15

• Cycle is a endogenous system but may be influenced by exogenous factors - cycles of other women.
• McClintock used sample of 29 women in her study who had history of irregular periods.
• Samples of pheromones were obtained from 9 of the women who at different stages of cylce.
• Done via cotton pads worn in p armpits for 8 hours minimum.
• Pads were treated with alcohol and frozen to be rubbed on upper lip of the other p.
• On first day pads from start of menstrual cycle were applied to all 20 p, on second day they were given a pad from second day of cycle and so on.
• Found that 68% of women experienced changes to their cycle that brought them closer to cycle of their odour donor.

Question 16

Seasonal Affective Disorder - SAD

Answer 16

• Depressive order that is triggered during the winter when number of daylight hours becomes shorter.
• Main symptoms are persistent low mood, lack of activity and interest in life.
• Type of infradian rhythms called a circannual rhyhtm as it may be due to distruption of sleep wake cycle and this is result of long periods of daily darkness during winter.
• Melatonin appears to cause it.
• At night pineal gland secretes melatonin until dawn where there is increase in light
• In winter, lack of light in morning means secretion process goes on longer.
• Affects production of serotonin which is linked to depression.

Question 17

Evaluation of infradian rhythms - supporting evidence

Answer 17

• Wealth of it.
• McClintock study provides supporting evidence that menstruation, despite being controlled by internal hormones can be influenced by external pheromones in sweat as well.
• Strength - shows infradian rhythms are controlled and affected by internal and external factors.

Question 18

However - supporting evidence

Answer 18

• Disagreement about whether human pheromones even exist, and extent to which they can have an effect that still requires research.
• Casts doubt on whether they do control infradian rhythm of monthly cycle in women.
• Stress, changes in diet, exercise can all affect menstrual cycle. Synchronisation in McClintock study may have occurred due to chance.
• Study had a small sample and relied on p self report of onset of own cycle.
• Weakness - all factors cast doubt on support for evolutionary basis of menstrual cycle.

Question 19

Evaluation of infradian rhythms - evolutionary basis of menstrual cycle

Answer 19

• Synchronised menstrual cycle means there could be synchronised pregnancies.
• Childcare could be shared when babies are born around same time.
• Strength - evolutionary advantage provides evidence for phermomones controlling infradian rhythms.

Question 20

However - evolutionary basis of menstrual cycle

Answer 20

• Wilson challenges idea of menstrual synchronicity, stating that experimental evidence of its existence was exaggerated, casting doubt on phenomenon.
• Schank aruged if too many females synchronising together, produce competition for highest quality males at the same time.
• Weakness - casts doubt on evolutionary basis of synchronisation as avoidance of synchrony would appear the most adaptive strategy to be naturally selected.

Question 21

Evaluation of Infradian Rhythms - Practical application

Answer 21

• Effective treatment for SAD is phototherapy - lightbox that stimulates strong light in morning and evening.
• Resets melatonin levels in people with SAD.
• Strength - adds support to idea that melatonin plays a role in SAD and this has provided relief for sufferers, improving quality of lives.
• By using light box as opposed to taking anti depressants this will avoid side effects.

Question 22

Ultradian Rhythms

Answer 22

• Last less than one day
• Cycle of NREM and REM sleep over the sleep period.
• Person first experiences NREM sleep followed by a shorter period of REM sleep.

Question 23

REM sleep

Answer 23

• 4 stages.
• Shallow stages - 1 and 2
• Deep or slow wave sleep - 3 and 4
• Complete cycle consists of progression through 4 stages of NREM sleep before entering a final stage of REM sleep then cycle starts again.
• Brain waves can be measured using an EEG which can distinguish between stages of sleep.
• As sleeper goes through sleep stages of brain waves become less frequent but bigger in size.
• EMG and EOG are also used to measure muscle and eye movements.

Question 24

REM sleep

Answer 24

• Has fast desynchronized EEG activity that is like the awake state.
• Cycles continue through the night with SWS getting shorter in time and REM sleep getting slightly longer as night goes on.
• Each cycle approx 60 minutes during infancy and 90 minutes during adolescence.
• Can also be as long as 110 minutes.
• Number of sleep cycles depends on how long an individual sleeps for.
• Be about 5 full cycles in a full night sleep.

Question 25

Evaluation of Ultradian Rhythms - evidence to support distinct stages in sleep

Answer 25

• REM sleep linked to dreams as when people are awoken during this stage of sleep they can often recall their dreams.
• Dement and Kleitman monitored sleep patterns of nine adults. 7 males and 2 females all from USA no age or gender details recorded.
• 5 p studied in detail and 4 were studied to confirm results. 5 stayed between 6-17 nights and 4 stayed between 1 and 2 nights in a sleep lab. Used an EEG to record brain wave activity Controlled for effects of caffeine and alcohol. REM activity during sleep was highly correlated with experience of dreaming. Found that brain activity varied according to how vivid dreams were and p woken during dreaming reported very accurate recall.
• Strength - suggests that REM is an important component of the ultradian sleep cycle. Provides evidence that there is different activity at different stages during sleep. Allowed study of dreams in a more objective way as there was a definite physiological state that represented dreaming.

Question 26

However - evidence to support distinct stages in sleep

Answer 26

• Not all individuals can recall dreams when awoken in REM sleep.
• Dement and Kleitmen found that people reported dreams during NREM sleep but less often.
• Weakness - casts doubt on strength of the link between this sleep stage and activity that is suggested to occur within it.
• Sample size and make up in the original study has been criticised. Means supporting evidence for idea of distinct stages of sleep is limited in terms of generalistion.

Question 27

Evaluation of Ultradian Rhythms - scientific methodology

Answer 27

• Procedures and measuring tools such as EEG are objective and not open to researcher basis.
• As p is asleep there is little opportunity for demand characteristics to effect results.
• Strength - means research is scientifically robust, reliable and valid.

Question 28

However - Scientific methodology

Answer 28

• Study has been replicated many times by them and other researchers adding further evidence to idea of distinct stages of sleep.