biological rhythms, endogenous pacemakers and exogenous zeitgebers Flashcards
what is a biological rhythm?
a distinct pattern of change in body activities that conform to cyclical time periods
what 2 things are all biological rhythms governed by?
endogenous pacemakers
exogenous zeitgebers
how long do circadian rhythms last for?
24 hours
what are 2 examples of circadian rhythms?
the sleep/wake cycle
core body temperature
what is the important exogenous zeitgeber that makes us feel drowsy at night and alert during the day (the sleep/wake cycle)?
daylight
who studied whether endogenous pacemakers may have an effect on the sleep/wake cycle?
Siffre
how did siffre study the effects of endogenous pacemakers on the sleep/wake cycle and what were the results?
he spent extended periods of time inside a cave, deprived of natural light and sounds
he found his ‘free running’ biological rhythm settled to one that was just beyond 24 hours (around 25 hours), though he continued to fall asleep and wake up on a regular schedule
who found similar results to Siffre’s cave study?
Aschoff and Wever
what do Siffre and Aschoff and Wever’s results suggest?
the ‘natural’ sleep/wave cycle may be slightly longer than 24 hours, but it is entrained by exogenous zeitgebers associated with our 24 hour day (e.g. meal times, number of daylight hours)
why does research into the sleep/wake cycle have economic implications?
it shows us how to best manage worker productivity
shift workers are more likely to have poorer health and night workers are more likely to make more mistakes/have more accidents
how has research into circadian rhythms helped with drug treatments?
because circadian rhythms co-ordinate body functions such as heart rate, digestion and hormone levels, it has an effect on pharmacokinetics (the actions of drugs on the body and how well they are absorbed and distributed)
why are the studies into circadian rhythms usually ungeneralisable?
small-scale studies and case studies are used- unrepresentative of the general population
what did Siffre find as he got older? what implications does this have?
at the age of 60 his internal clock ticked much slower than it did when he was young.
even when the same person is involved, there are factors which may prevent general conclusions being drawn
what is one major issue in Siffre’s study which may have effected his results?
the use of artificial light- which he turned on when he woke up and turned off when he went to sleep
what did Czeisler et al find in terms of individual differences in circadian rhythms?
individual’s sleep/wake cycle can vary from 13 to 65 hours
what are infradian rhythms and 2 examples?
a type of biological rhythm with a frequency of less than one cycle in 24 hours
menstruation and seasonal effective disorder
what are ultradian rhythms?
what is an example?
a type of biological rhythm with a frequency of more than one cycle in 24 hours
sleep stages
what is the menstrual cycle (an infradian rhythm) governed by?
monthly changes in hormone levels which regulate ovulation
how long (approximately) is the menstrual cycle?
28 days
what happens in the menstrual cycle?
rising levels of 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, and the womb lining comes away and leaves the body (the menstrual flow)
is the menstrual cycle an endogenous or exogenous system?
endogenous
what did McClintock and Stern find regarding menstrual cycles?
menstrual cycles may synchronize as a result of the influence of other female’s pheromones
exogenous factors can effect the timing of the menstrual cycle
what was McClintock’s procedure into menstrual cycle synchronization?
29 women with irregular periods
samples of pheromones were taken from 9 women who were at different stages of the menstrual cycle via a cotton pad on their armpit
pads treated with alcohol and frozen to be placed on the upper lip of the other women
on day one, pads from the start of the cycle were applied to the other 20 women, on day 2 pads from the second day were applied etc.
what were the findings from McClintock’s study?
68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’
what are the main symptoms of seasonal affective disorder (SAD)?
persistent low moods and a general lack of activity and interest in life
when is SAD triggered and why?
in the winter months
because the number of daylight hours are shorter
what is the specific type of rhythm that SAD can be classed as other than infradian and why?
circannual rhythm
because it is a yearly cycle
why can SAD also be referred to as a circadian rhythm?
as SAD may be due to the disruption of the sleep/wake cycle, due to the prolonged daily darkness during winter
what have psychologists hypothesised is the cause of SAD?
during the night, the pineal gland secretes melatonin until dawn when there is an increase in light. during winter, the lack of light in the morning means this secretion process continues for longer. this is thought to have a knock on effect on the production of serotonin in the brain- a chemical that has been linked to the onset of depressive symptoms
how many stages of sleep are there and how long does it take to get through the stages?
5 stages
roughly 90 minutes
what is each stage of the sleep cycle characterised by?
different level of brainwave activity
how can these sleep stages be monitored?
using an EEG
what is stage 1 and 2 called and what waves are associated with them?
light sleep
theta waves
what is stage 3 and 4 called and what waves are associated with them?
deep sleep/slow wave sleep
delta waves
what is stage 5 and what happens in it?
REM (rapid eye movement) sleep
the body is paralysed yet brain activity speeds up significantly
what is the evolutionary basis of the menstrual cycle?
for our ancestors it may have been advantageous for females to menstruate together and therefore fall pregnant around the same time, and could look after the children collectively
why has the validity of the evolutionary basis of the menstrual cycle been questioned and according to who?
the avoidance of synchrony would be the most adaptive evolutionary strategy according to Schank
what are extraneous variables that may have effected the results of McClintock’s study?
stress, changes in diet, exercise, etc.
who failed to find any evidence of menstrual synchrony in all female samples?
Trevathan et al
what did Dement and Kleitman find in their study on the sleep stages?
REM sleep was highly correlated with the experience of dreaming, brain activity varied according to how vivid dreams were, and participants woken during dreaming reported very accurate recall of their dreams
does Dement and Kleitman’s study support the sleep cycle?
yes
what has research into SAD helped develop?
a treatment- phototherapy
what is the suprachiasmatic nucleus (SCN) and where is it located?
a tiny bundle of nerve cells
located in the hypothalamus in each hemisphere of the brain
is the SCN a primary endogenous pacemaker?
yes
what type of rhythm is the SCN influential in maintaining?
circadian
how does the SCN receive information about light?
what does this enable our biological clock to do?
nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual area of the cerebal cortex. the SCN lies just above the optic chiasm. this is how it receives information about light, which continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep
what did DeCoursey et al. do to chipmunks in their study of the sleep/wake cycle?
destroyed the SCN in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days. the sleep/wake cycle of the chipmunks completely disappeared and by the end of the study a significant amount of the chipmunks had been killed by predators
what did Ralph et al do in their study using hamsters?
they bred ‘mutant’ hamsters with a 20 hour sleep/wake cycles. when the SCN cells from the foetal tissue of mutant hamsters were transplanted into the brain of normal hamsters, the cycles of the second group defaulted to 20 hours
what do both DeCoursey et al. and Ralph et al’s studies emphasise in terms of the SCN?
emphasise the role of the SCN in establishing and maintaining the circadian sleep/wake cycle
what is the structure of the pineal gland and where is it located?
a pea-like structure
just behind the hypothalamus
where does the SCN pass the information on day length and light that it receives?
to the pineal gland
what does the pineal gland increase production of during the night and what does it do?
melatonin
its a chemical that induces sleep
what has melatonin been suggested to have a casual link to (infradian rhythm)?
SAD
what are endogenous pacemakers?
internal body clocks that regulate many of our biological rhythms
what are exogenous zeitgebers?
external cues that may affect or entrain our biological rhythms
what are the 2 main exogenous zeitgebers?
light
social cues
what main endogenous pacemaker can light reset?
the SCN
what key processes in the body can light have an indirect influence on?
hormone secretion
blood circulation
what did Campbell and Murphy demonstrate in their study of how light effects the sleep/wake cycle and how did they do it?
they demonstrated that light may be detected by skin receptor sites on the body even when the same information is not detected by the eyes
15 participants were woken up at various times and a light pad was shone on the back of their knees. the researchers managed to produce a deviation in the participant’s sleep/wake cycle by up to 3 hours
