Biological Rhythms and Sleep

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  • Created by: Amy
  • Created on: 14-01-13 17:01
What is a circadian rhythm?
A rhythm that occurs approx daily
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What is an infradian rhythm?
Long, slow rhythms that occur less than once every 28 hours
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What is an ultradian rhythm?
Short, faster, cycling rhythms which occur more than once a day
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Why have these evolved through natural selection?
To allow animals to predict and behaviour appropriately in the natural world
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What two things do biological rhythms need to work effectively?
Exogenous zeitgebers and endogenous pacemakers
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What are endogenous pacemakers?
A body clock; they are internal cues that keeps time and biological rhythms following a regular pattern
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What are exogenous zeitgebers?
Time givers; they are external cues like the sun
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What are some examples of circadian rhythms?
The body temperature cycle and sleep/wake cycle
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What are circadian rhythms (and other rhythms) controlled by?
An endogenous pacemaker
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Where is this located?
In the suprachiasmatic nucleus in the hypothalamus
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What is the SCN linked to?
Light receptors in the eye, and the pineal gland
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How is the sleep/wake cycle reset?
When light reaches our eye (exogenous zeitgeber)
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In Silver's study, which part of the brain was removed?
The SCN
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What was the effect on the hamster's circadian rhythms?
It causes irregular activity; lost their daily pattern
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What does this show?
That the SCN controls your circadian rhythms
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What does this not prove?
That, on its own, the SCN is the body clock
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By removing the SCN, what else could have happened?
Researchers could have damaged other areas nearby which damaged the activity cycle
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In Silver's second study, what was implanted into the hamster's brains?
Fetal tissue of the SCN
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What was the effects on the hamsters?
after a few days the regained normal circadian rhythms
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What is a strength of Silver's study?
Causal relationship between the SCN and bio rhythms therefore supporting endogenous pacemaker's role in bio rhythms
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What are weaknesses of Silver's study?
Use of animals (difficult to generalise to humans, ethics)
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Where did Siffre carry out his study?
A cave in Texas
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How long for?
7 months
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What did he measure?
Vital functions (sleeping, blood pressure/temperature)
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What were his main findings?
His daily rhythms occurred on a 25-hour clock
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What is the evidence for an endogenous pacemaker?
He still had a cycle without exogenous zeitgebers
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Evidence that an exogenous zeitgeber is needed?
We have 25-hour clock, so we need exogenous zeitgeber to keep our clock regular
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What are strengths of Siffre's study?
High internal validity (removes all exogenous zeitgebers); psychology as a science: objective measuring to monitor bio rhythms therefore more reliable approach
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What are the weaknesses of this study?
Difficult to generalise to other people because there was a restricted sample
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What are examples of infradian rhythms?
hibernation, breeding, menstruation,
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What did Pengelly and Asmundson study?
Carried out a study on squirrels, which hibernate in the wild. Five squirrels were blinded by birth and spent their life in constant darkness and temperature with plenty of food
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What did they find?
For the next 4 years the squirrels hibernated at roughly the same time as wild animals. This is a clear demonstration of an endogenous bodily rhythm. Their body clocks were not completely accurate as some of them hibernated a bit earlier
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What is the evidence for the endogenous pacemaker?
The still hibernated even without exogenous zeitgebers
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What is the evidence for exogenous zeitgebers?
Their body-clocks were not completely accurate as wild animals
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What are the strengths of this study?
High internal validity; not reductionist as explains both exogenous zeitgebers and endogenous pacemakers
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What are the weaknsses?
Can't generalist to humans(we don't hibernated); ethical issues - cruel
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What is SAD?
A form of depression that in some people repeatedly occurs during the winter months.
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What does this suggest?
It may be associated with the abnormalities of biological rhythms
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How is this supported?
Light therapy and treatment with melatonin can be helpful
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Why does this suggest that exogenous zeitgebers exist?
People with SAD are affected by the lack of light and are helped by light therapy
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What happened in Russell's study about the menstruation cycle?
He found that if sweat from a donor woman was rubbed onto the lips of a recipient woman, eventually the menstrual cycles of donor and recpient would synchronise
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Why is this so?
Pheremones in the sweat were picked up by the recipient and these altered the menstrual cycle
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What is the evidence for an endogenous pacemaker?
They would still have their period if they didn't synchronise
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What is the evidence for exogenous zeitgebers?
The sweat synchronised their periods
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From an evolutionary perspective, why would it be advantageous for women living together to have synchronised periouds?
All women would be fertile at the same time
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Why is this study not reductionist?
Explains exo and endo
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What is an example of an ultradian rhythm?
Sleep/wake cycle
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What two factors of life cause considerable disruption of our biological rhythms?
shift work and jet lag
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What rhythms does shift work disrupt?
Circadian
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Why?
Because it makes people work when they would normally be asleep, which disrupts the cycle of sleep and wakefulness and forces people's bodies and minds to adapt to a new pattern
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Why could shift workers be in a state of internal de-synchronisation for days?
Because different biological rhythms like body temperature and digestion all adapt at different speeds
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Why is it important to consider the impact of shiftwork?
20% of people in America work shifts; because of people being tired; because of accidents; most lorry accidents occur between 4-7am
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What is internal desynchronisation?
Where each cycle in the body takes a different amount of time to adapt to the new exogenous zeitgebers
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Where was Czeisler's study carried out?
A quarry
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Who were the participants?
Shift workers
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What was the original shift pattern?
Night, Day, Evening shifts
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What were the effects of this disruption of their circadian rhythms?
Thy were tired and the boss was concerned about their performance
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What was the shift pattern changed to?
Day, Evening Night at 3 weeks at a time
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What were the results?
If you’re working with the biological clock, it is much easier and causes less disruption (phase delay)
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What were the strengths of this study?
High internal validity, reflect real life (external validity)
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What are the weaknesses of this study?
Carried out in America (culture bias); low population validity (restricted to one profession)
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What are the implications of Czeisler's work?
People can be helped to adjust to shift work if we use our knowledge about circadian rhythms
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What did Coren suggest?
Rotating shift patterns every 2 or 3 days avoids even trying to adjust the circadian rhythm.
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However, what does this mean?
That our bodies are in a constant state of internal desynchronisation
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What did Gordon et al find in police officers?
They moved from backward to forward shifts which lead to a 30% reduction of sleeping on the job and 40% reduction in accidents at work
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What did Phillips find in Kentucky Police?
They chose from one of 3 8hr shifts so their body doesn't have to adjust to a new pattern
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What did Sack find?
provided places for planned napping but it wasn't popular with staff
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What is jet lag caused by?
Rapid travel across time zones by plane - too fast for the body to adjust
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What are the symptoms?
Extreme tiredness, slowness of mental and physical reactions
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Why does jet lag occur?
Your endogenous p's are out of sync with exogenous z's
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Why is there less disruption when flying East to West?
Our body runs on a 25 hr clock and it's easier to stay up a few more hours than go to bed when we're not tired
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Who did Schwartz study?
US baseball teams; some were travelling west to east, some travelling east to west
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Who had the best performance?
Those who were travelling E>W, 44% of games one
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Which had the worst performance?
West to East with 37% games one
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Why is this?
Easier to phase delay than phase advance; suffering jet lag
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What is a weakness of this study?
Difficult to establish cause and effect - is it direction of travel or sporting ability?
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What are some techniques that are shown to reduce jet lag(coren)?
Sleep well before flight so you're not sleep deprived; anticipate the time on arrival (e.g. if in daylight, stay awake on the plane); avoid stimulants, go into daylight as soon as possible as it resynchronises your body clock
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Other cards in this set

Card 2

Front

What is an infradian rhythm?

Back

Long, slow rhythms that occur less than once every 28 hours

Card 3

Front

What is an ultradian rhythm?

Back

Preview of the front of card 3

Card 4

Front

Why have these evolved through natural selection?

Back

Preview of the front of card 4

Card 5

Front

What two things do biological rhythms need to work effectively?

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Preview of the front of card 5
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