Biological Rhythms 1

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  • Created by: Sarah
  • Created on: 20-04-13 16:49

Circadian Rhythms

Outline Circadian rhythms 

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Circadian rhythms

  • 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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Ultradian rhythms

Outline ultradian rhythms 

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Ultradian rhythms

  • 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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Infradian rhythms

Outline Infradian rhythms 

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Infradian rhythm

  • 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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