Circadian rhythms Flashcards
what are circadian rhythms?
a pattern of behaviour that occurs or recurs approximately every 24 hours and which is set and reset by environmental light levels
what are our circadian rhythms drive by?
body clocks, found in all cells of the body and synchronised by the master circadian pacemaker SCN found in the hypothalamus.
Why must these pacemakers constantly be set?
so our bodies are synchrony with the outside world
How do our bodies keep in synchrony with the outside
light provides the primary input to this system, setting the body clock to the correct time in a process termed photoentrainment. The most familiar of the circadian rhythms subject to this entrainment process is the sleep-wake cycle
what is the sleep-wake cycle?
refers to the alternating states of sleep and waking that are dependant on the 24-hour circadian rhythms
what are the external signals in the sleep wake cycle?
light and darkness. The circadian rhythms also dips and rises at different times of the day.
what are other circadian rhythms
core body temperature is one of the best indicators of the circadian rhythms. It is at its lowest about 36 degrees at about 4:30 am and its highest about 38 degrees about 6pm
name a second circadian rhythms
Hormonal release
the production and release of melatonin from the pineal gland in the brain follows a circadian rhythm with peak levels which happens during hours of darkness.
Case study of Michael Siffre
Siffre subjected himself to himself to long periods of time living underground in order to study circadian rhythms
While living underground he had no external cues to guide his rhythms. The only thing that influenced his behaviour was his internal clock
After his first underground stay of 61 days in the southern Alps in 1962, he resurfaced on 17 September believing the date was August 20th
His circadian rhythm settled down to just over 24 hours
Name a first evaluation point
Hughes 1977 shows research support for light
He tested four participants stationed at the British Antarctic station
In Feb the end of the antarctic summer cortisol levels followed the familiar pattern reaching their highest point as participants woke and their lowest point when they went to bed
However, after three months of continuous darkness this pattern changed with the peak levels at noon rather than as they woke
This shows that extreme daylight is responsible for the circadian rhythm
Name a second evaluation point
Research support for individual differences in circadian rhythms
Czeisler et al 1999 circadian rhythms can vary from 13 hours to 65 hours which concludes that individuals appear to be innately different in terms of when their circadian rhythms reach their peak
Duffy et al in 2001 said that individual differences would explain why some people prefer to rise early and go to bed late (6am to 10pm) whereas some people prefer to wake up late and go to bed late
(10pm 1am)
Name third AO3 point
There was a flaw in earlier research methodology for the circadian rhythm
In most studies participants were isolated from variables that might affect their circadian rhythm such as clocks, radios and daylight
However, they were not isolated from artificial light because it was believed that dim artificial light in contrast to daylight would not affect their circadian rhythms
However, there is research support which suggests that this might not be true. Czeisler et al 1999 altered circadian rhythms from 22 hours to 28 hours by using dim artificial light
Name a fourth AO3 point
There are real life applications
Chronotherapeutics - the study of how timing affects drug treatments
It is essential that the right concentration of a drug is released into the target area of the body
For example, the risk of a heart attack is greater in the morning
Evans and Martin (1996) found that as a result of this chronotherapeutic medication has been developed which can be administered before the person goes to sleep at 10pm but the actual drug is not released until the morning 6pm
Name a final AO3 point
Temperature may be more important than light in setting the circadian rhythm
Buhr et al in 2010 argues that temperature is more important than light
Although light may be the trigger, the SCN transforms information about light levels into neural messages that set the body’s temperature
Body temp can fluctuate on a 24hour circadian rhythm and even small changes in body temperature can send powerful signals to our body clock
Buhr et al found that these fluctuations in temperature set the timing of cells in the body, and therefore cause tissues and organs to become active or inactive
