Outline Circadian rhythms
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- Circadian rhythms last 24 hours.
- The sleep wake cycle is one circadian rhythm.
- An endogenous factor of this is the SCN, the body's masterclock, which works with the pineal gland to produce melatonin as night approaches.
- An exogenous factor is sunlight which entrains the body's 24 hour clock. Hormones and neurotransmitters cause the body to respond to different levels of light.
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Outline ultradian rhythms
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- Ultradian rhythms last less than 24 hours, including the different stages of sleep.
- There are 5 sets of 90 minute cycles.
- The first four stages are NREM sleep and the final stage is REM sleep which is also the stage in which we dream.
- The first stage has EEG activity characterized by alpha waves.
- The second stage has EEG activity characterized by theta waves.
- The third and fourth stages have EEG activity characterized by delta waves.
- There is slow wave sleep during the fourth stage.
- The endogenous factor is the RAS which prevents muscle movement.
- The other endogenous factor is the thalamus which prevents sensory information entering the brain.
- The exogenous factors are sunlight and temperature.
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Outline Infradian rhythms
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- One example of an infradian rhythm is the menstrual cycle which lasts longer than 24 hours.
- The endogenous factor is the pituatry gland which releases FSH and LH and these cause oestrogen and progesterone to be released in the ovaries.
- The exogenous factor is pheromones, which are also known as external hormones, that cause the synchronisation of others' infradian cycles.
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