AO1 - Ultradian Rhythms

• An ultradian rhythm occurs more frequently than once every 24 hours (4-7 cycles per night) - it is shorter than 24 hours, e.g. the stages of sleep
• The cycle lasts approximately 90 minutes and consists of 5 stages - a person can experience up to 5 cycles per night that repeat in a rhythmic pattern
• Stages 1+2 - light sleep where a person can be easily woken (NREM):

  • Stage 1 - Alpha waves, decrease in body temperature and heart rate
  • Stage 2 - Alpha waves continue but there are occasional random changes in pattern called sleep spindles, these are a reaction to external noises called k-complexes
• Stages 3+4 - known as deep sleep or slow wave sleep (NREM):

  • Delta waves with lower frequency and higher amplitude
  • It is difficult to wake someone up
  • Brain is recovering
• Stage 5 - REM:

  • Theta waves and the eyes occasionally move around
  • Body is paralysed
  • Brain activity is like being awake
  • Dreams are often experienced