Circadian Rhythms Flashcards
What is a biological rhythm
A change in the body processes or behaviour in response to cyclical changes within the environment
What are circadian rhythms
Biological rhythms that have a periodicity of 24 hrs
What is a sleep waking cycle
One period of sleep and one period of waking every 24 hrs
What are core body temperatures
One peak and trough every 24 hrs
What is hormone production
Melatonin levels peak in the dark and are at its lowest during daylight
What do photosensitive retinal ganglion cells do
Detect the brightness of our surroundings and send information to the optic nerve to the Suprachaismatic Nuclei (brain’s master clock)
What is the SCN (that nuclei shi im not writing out again)
The brain’s master clock that governs everything in our body to sleep and wake (cycles)
What are our circadian rhythms driven by
Our body clocks found in all cells of the body and synchronised by the master circadian pacemaker (SCN) found in the hypothalamus
Must constantly be reset so that our bodies are in synchrony w the outside world
Light provides primary input to this system setting the body clock to the correct time in a process termed photoentrainment
What do photosensitive cells do
Contribute to the regulation of pupil size and other behavioural responses to ambient lighting conditions
Does the body make and keep its own circadian rhythms
Yes, natural factors in your body produce circadian rhythms. For humans, some of the most important genes in this process are the Period and Cryptochrome genes. These genes code for proteins that build up in the cell’s nucleus at night and lessen during the day
What is the body’s internal body clock that regulates biological rhythms
Endogeneous pacemakers
What are the external factors in the environment which reset our biological clocks
Exogenous zeitgebers
How do circadian rhythms affect body function and health
Hormone release
Eating habits
Digestion
Body temperature
Too much light can be detrimental (diabetes, depression)
What are ultradian cycles
More than once in 24 hrs - sleep cycle, for example
What are infradian cycles
Less than once a day - menstrual cycles. for example
How much does our body temperature vary during the day
2 degrees celsius
Lowest at 4am
Peak approximately 6pm
Warmer we are, the better we perform
Describe Siffre’s 1962 cave study
Siffre spent 2 months living in total isolation in a subterran cave without access to clock, calendar or sun
Sleeping and eating only when his body told him so, goal was to discover how the natural rhythms of human life would b affected by living “beyond time”
His body clock remained the same despite being a lil caveman
Describe Siffre’s 1972 cave study
kid cudnt stay away from the bats
Spent 6 months in Texan cave
Wud turn on lighting when he awoke and turned off in evening when wanted to sleep (no external light source)
Circadian sleep-wake cycle became longer than 24 hrs
Was also inconsistent (between 25-32 hrs), days r therefore longer
179 actual days passed, but 4 him was only 151 days
Body temp. was fairly consistent
Had depression n suicide thoughts (due to isolation not sleep deprivation as slept whenever he liked)
What does Siffre’s study show
Circadian rhythm maintained without exogenous zeitgebers
Npot perfectly regulated tho
Must b at least 2 body clocks (sleep-wake cycle and body temp.)
What was Aschoff and Rutger’s 1976 study that confirmed Siffre
Placed participants in a bunker for 4 weeks w no natural light
Settled into a sleep/wake cycle of between 24 n 25 hrs (apart from one which extended to 29 hrs)
What do both Siffre and Aschoff suggest
Natural light sources in the environment are vital for keeping the individual to a 24 hr sleep cycle
Describe Folkard et al 1985 study
Isolated 12 participants from natural light for 3 weeks (dark cave), manipulating the clocks that only 22 hrs passed a day
None of the participants cud adjust comfortable to the pace of the clock except one
This shows the strength of the circadian rhythm as a free-running cycle and questions the extent to which it can b overridden by exogenous zeitbegers
Evaluate Folkdar’s study
Difficult to generalise findings from studies of the sleep/wake cycle because individual cycles can vary, in some cases 13-65 hrs
the fuck
i am in the bottom of this spectrum
and every other spectrum…
There are also differences in the sleep/wake cuycle
Where is melatonin secreted
In breast milk
But varies throughout the day to help a baby know when to sleep or wake
What can happy to babies who are fed formula instead of breast milk
Find it harder to regulate their sleep
What is SCN
Suprachiasmatic nucleus
Tiny bundle of nerve cells located in the hypothalamus in each hemisphere in the brain
One of primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms
Nerve fibers connected to the eye cross in an area called optic chiasm on their way to the visual area of the cerebral cortex
Receives info about light directly from this - even when our eyes are closed
What is entrainment
Process of resetting the biological clock in line w external time cues
Synchronises circadian rhythms
Talk abt melatonin and cortisol roles in sleep/wake cycle
Melatonin triggers sleepiness in a dark environment of a typical physiological setting, and cortisol secretions sustain daytime consciousness throughout the morning
Describe DeCoursey’s animal study on SCN
Decoursey et al 2000 - destroyed in the SCN connections in the brains of 30 chipmunks, who were then returned to their natural habitat an observed over 80 days
The sleep/wake cycle of the chipmunks disappeared and by the end of the study, a significant proportion of them had been killed by predators (due to being awake and vulnerable, when should have been asleep)
Describe Ralph’s animal study on SCN
Ralph et al 1990 - bred ‘mutant’ hamsters with a 20-hr sleep/wake cycle. When SCN cells from the foetal tissue of mutant hamsters were transplanted into brains of normal hamsters, cycle of the second group defaulted to 20 hrs
How did Burgess et al study jet lag using light exposure to avoid it (practical application of exogenous zeitgebers)
Found that exposure to bright light prior to an east-west flight, decreased the time needed to readjust to local time on arrival
Participans were exposed to continuous bright light shifted their circadian rhythm by 2.1 hrs whereas those exposed to intermittent bright light shifted their rhythm by 1.5 hrs and those exposed to dim light shifted theirs by just 0.6 hrs
As a result, participants in the 1st conditions felt sleepier 2 hrs earlier in the evening and woke 2 hrs earlier in the morning i.e. closer to local time conditions
What are social cues for circadian rhyth,s
About 6 weeks of age, rhythm begins and by 16 weeks, most babies are entrained
Schedule imposed by parents said to have large influence here including adult-determined mealtimes and bedtimes
Jet leg - research has suggested that adapting to local eating and sleeping times is an effective way of entraining circadian rhythms