Biological rhythms

circadian rhythms

consistent rhythms over a period of 24 hours e.g. sleep-wake cycle, body temperature, metabolism

endogenous pacemaker

internal time keeper

exogenous pacemaker

external time keeper

External/environmental cues that entrain/synchronise an organisms biological rhythms to earths 24 hour e.g. light/temperature/eating pattern

Part of brain thought to be internal body clock

suprachiasmatic nucleus (SCN)

A small area of the hypothalamus

Outline how the suprachiasmatic nucleus controls our sleep-wake cycle

influenced by external factors (light) the SCN receives info about light from the price nerve and passes info about changes in light levels to the pineal gland and controls the release of melatonin (sleepy)

Outline the findings of one study which supports the idea of an internal body clock

morgan found when hamsters had their SCNs removed their sleep-wake cycle circadian rhythms disappeared. The rhythms were reestablished when SCN cells were transplanted from foetal hamsters (however can’t generalise to humans as hamsters have diff brain structures and are nocturnal)

Outline the findings of a study to support exogenous pacemakers

Miles et al found a man who was blind from birth (lacking zeitgeber of light) had a circadian rhythm of 24.9 hours which he found difficult to modify despite exposure to clocks and social cues. He had to take stimulants and sedatives t9 get 24 hour biological rhythm

Outline procedure, results and conclusion of Siffre study

procedure- spent 6 months alone in an underground cave and had contact with the outside world via telephone but had no idea what time it was- his behaviour was monitored e.g. when he slept and woke, and when he ate his meals- when he was awake researchers Put lights on and turned it off when he went bed- a range of psychological measurements were taken regularly

Results- his sleep/wake cycle at first was erratic then settled to a periodicity of around 25 hours- when he emerged it was the 179th day but by his days it was 151st

Conclusions- results indicate presence of an endogenous pacemaker as he settled for a regular cycle: also highlights importance of exogenous zeitgebers in maintaining a 24 hour cycle

Outline one issue with using the findings of studies such as miles et al and siffre to support the role of exogenous pacemakers

may be two separate systems which control our circadian rhythms. Apart from total isolation experiments which are artificial, there is never a time when the internal and external cues are separated so the running of a biological clock is likely to be a combined endogenous/exogenous exercise

Infradian rhythms

Consistent cyclical variations in physiological processes that repeat in time over a period of longer than 24 hours e.g. menstrual cycle, seasonal effective disorder

Ultradian rhythms

consistent cyclical variations in physiological processes that repeat in time over a period of less than 24 hours e.g. sleep cycle

Menstrual cycle as an infradian rhythm

occurs over an average of 28days but there is variation.

1. After menstruation, FSH and LH stimulate a follicle in one ovary causing an egg to ripen leading to production of oestrogen

2. Once egg has ben released the ruptured follicle starts to secrete progesterone causing the lining of the womb to become engorged with blood preparing for pregnancy

3. About two weeks later, if egg is not fertilised, then the lining of the womb is shed

Internal control- endocrine system (hypothalamus and puitary glang- control release of FSH, LH, oestrogen and progesterone)

External influence- stress, diet, exercise, other people’s pheromones

Study to support menstrual cycle as an infradian rhythm

Stern and McClintock

Found 68% participants experienced a change in their menstrual cycle that brought them more in line with their ‘odour donor’. Suggests external factors (phermone) can influence menstrual cycle

Criticism of study to support menstrual cycle as infradian rhythm

68% is not a large percentage so the results only apply to some women meaning individual differences play a part in the menstrual cycle

Seasonal affective disorder as an infradian rhythm

Mental disorder characterised by the symptoms of depressions in a seasonal cycle (usually winter when days are shorter)

External factors- winter months it gets light later meaning melatonin may continue to be secreted later into the day

Internal factors- as not everyone gets SAD it implies there may be some fault with endogenous pacemaker system (is it not sensitive to subtle changes in light)

Study to support seasonal affective disorder as an infradian rhythm

Sanassi

80% of people with SAD experience a reduction in symptoms when using light therapy. This suggests that diminished light levels is a factor in SAD and therefore this research has useful RLA

Criticise the study to support SAD as an infradian rhythm

light therapy doesn’t work for 20% people so individual differences must be involved suggesting light isn’t a factor in SAD and instead other factors involved in addition to light, for these 20% e.g. colder

Sleep cycle as a ultradian rhythm

Stages 1 and 2: mostly alpha and theta waves, short time, light sleep, heart rate slows and temperature drops, muscles relax

Stages 3 and 4: delta waves, very deep sleep, lasts 40mins, body temp bp pulse all at lowest, body repair

REM SLEEP: rapid eye movement, beta waves are similar to being awake, muscles paralysed, hard to awaken, dreams occur, enable brain recovery

Stage 1 + 2→ stage 3+ 4→ stage 3→ stage 2→ REM

Real life application for sleep cycle as a ultradian rhythm

sleep hygiene

Understanding age-related sleep changes that has led to strategies that older people can use to improve sleep, research shows that older people experience less stage 3 and 4 sleep, medication and relaxation techniques

Weakness of sleep lab experiments

lack ecological validity→ carried out in artificial environments such as hospitals where researchers are continuously monitoring patients who are hooked up to machines meaning they are limited yo movement they can perform meaning the patient will most likely sleep different so we cannot be sure the participants sleep cycle pattern work similar in real life