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Biological Rhythms

Circadian Rhythms - Occurs once every 24 hours eg. sleep-waking cycle

Infradian Rhythms - Less than once every 24 hours eg. Menstrual cycle

Ultradian Rhythms - More than once every 24 hours eg. washing hands.

Endogenous pacemaker - Some aspects of biological rhytms set by genetically determined biological structures within the body. The SCN located in the hypothalamus acts as an internal clock keeps the body on a 24 sleep-waking cycle. It senses light and regulates the pineal gland which secretes the hormone melatonin which induces sleep. LESS LIGHT means more melatonin and sleeping occurs. Menaker et al (78) lesioned this structure in hamsters, disrupting their sleep waking cycle.

Exogenous zeitgebers - External influences that act like a prompt which may trigger biological rhythm. The most important EZ is light. Siffre (75) spent 6 months in a cave where he had no clocks or natural light. His sleep-waking cycle extended from a 24 hour to a 25-30 cycle.

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Biological Rhythms

EP and EZ intereact to regulate the timing of our biological rhythms.

Studies have shown EP to completely determine a cycle. Pengelly and Fisher found that squirrels hibernate even when kept in labratory conditions, which are very different to their natural environment.

Humans can change the environment to suit their needs. EG, using articficial light to keep us awake.

Cultural factors - Eskimos live in permanent daylight or permanent night-time but still manage to regulate their daily sleep cycles.

Individual differences - Studies show that although some peoples cycles are disturbed, otheres can maintain a regular sleep-waking cycle.

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Disrupting Biological Rhythms

1. Natural environment zeitgebers normally change slowly, eg. light levels during the year gradually change.

2. However, in modern society, they can change quickly. Thia can cause negative effects on our ability to function - slowing reaction times, impairing problem-solving skills and limiting our ability to concentrate.

JET LAG - Wegman et al found that travelling from east to west (phase delay) seems easier to adapt to than travelling west to east (phase advance).

SHIFT WORK - Czeiler et al studied workers at a factory whose shift pattern appeared to cause sleep and health problems. Researchers recommended 21-day shifts and changing shifts forwards in time (phase delay).

Research has limitations

Animal studies cannot be generalised to humans. Some studies lack validity as although natural light has been taken away, they have still been allowed artificial light. Individual differences - Speed each person can adapt may vary, difficult to determine cause or affect.

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Sleep States

EEG measures electrical activity in the brain

Adults pass through the stages about 5 times a night, each cycle lasting about 90 minutes.

Stage 1 - Like deep relaxation, with lowered heart rate, muscle tension and temp. Stage 2 - has slower and larger EEG waves, some quick bursts of high frequency waves (sleep spindles). Stage 3 - Larger, slower waves. Stage 4 - has the largest slowest waves of all, deepest stage of sleep. Metabolic activity is pretty low in general, and the sleeper is very hard to wake.

After stage 4, the cycle reverses back to stages 3 and 2. A period of active sleep occurs instead of stage 1. During the active stage, metabolic activity increases, the body appears almost paralysed except for REM. The EEG pattern s almost like when you're awake.

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Different Theories of Sleep - EVOLUTIONARY APPROAC

Webb - suggested that everyday sleep is similar to hibernation - sleep converses energy at times when it's harder to get resources. Using energy would be insufficient.

Meddis - suggested that sleep keeps animals safe. Keeping quiet and still, we are less likely to attract predators. However, sleep can make us more vulnerable to predators.

Not sleeping at all would be very advantageous, but it occurs in all animals, therefore it must have an important function - although how much we have varies. Animals the gaze often, sleep less to avoid predators, those that don't eat frequently and aren't hunted, sleep more!

- This approach helps us to understand how and why behaviours occur, which have evolved to help survival and adapt us to our environment.

- Evolution occurs over long periods, so it's hard to test theories about why some behaviours have been naturally selected, making them less useful from a scientific perspective.

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Oswald - suggested that non-REM sleep is for restoring bodily functions linked to physical activity and that REM is for restoring brain functioning.

Horne - suggested that there are two types of sleep - core sleep, which is made stage 4 (for body restoration) and REM (brain restoration) and optional sleep, which is made up of the other sleep stages. Optional sleep helps conserve energy.

- It seems that restoration does occur during sleep. Babies whose brains are developing spend more time in REM sleep and release more growth hormone during SWS.

- Long distance runners had more SWS sleep after a race, implying exercise increased the need for bodily restoration.

- However, HORNE and MINARD conducted a study where partcipants did physicaland cognitive activities. Although they fell asleep more quickly, they did not sleep for longer. May have been a reduction in their optional sleep.

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Techniques used in sleep research

- EEG measure electrical activity in the brain and provide quantitative reports which can easily be compared and have high reliabilty.

- EOGs measure electrical activity of the eyes, and EMGs of the muscles.

Self reports involve Ps keeping records of dreams and estimating the lengths. Limited by accuracy of recall.

Observations of patterns and directions of eye movement.

- Variables such as noise and distractions are controlled to increase reliabilty of research. However research in labratories creates an artificial environment and may affect Ps sleep patterns, decreasing validity.

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Sleeping patterns change during lifespan


The older we get, the less sleep we have.

Babies - 20 hours a day

Adults - 7-8 hours a day

50 + - 6 hours (average)

Elderly people more likely tow ake several times a night (Kales and Kales)

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