Biological Rhythms

• Biological Rhythms - a natural cycle of physical or behavioural changes in a living being influenced by internal processes and external factors, eg, day/night
• Circadian Rhythm - a pattern that occurs every approx. 24 hours and is reset by environmental light eg. sleep/wake, temperature
• Sleep wake cycle - refers to the alternating sleep and waking that are dependent on the 24 hour circadian cycle
• Circadian Rhythm:

  • Light is detected by the eye's optic nerve
  • Brightness level message is sent to the (SCN), found in the hypothalamus
  • SCN informs the pineal gland, which secretes melatonin causing us to become sleepy
• Endogenous Pacemaker (internal cues) - internal mechanism (SCN) that governs biological rhythms e.g sleepwake cycle
• Exogenous Zeitgeber (external cues) - External factors that are responsible for resetting the biological clock of an organism, eg. social cues (meal times), light
• Sleep Cycle (Stage 1): 5% (NREM)

  • light sleep
  • muscle activity slows down
  • alpha waves, progressing to theta waves
• Sleep Cycle (Stage 2): 50% (NREM)

  • Light sleep
  • Breathing/heart rate are slow
  • Theta waves begin
• Sleep Cycle (Stage 3): 10% (NREM)

  • Deep sleep begins
  • brain begins to generate slow delta waves
• Sleep Cycle (Stage 4): 10% (NREM)

  • very deep sleep
  • rhythmic breathing
  • brain produces delta waves
• Sleep Cycle (Stage 5): 25% (REM)

  • brainwaves speed up
  • dreaming occurs
  • breathing is rapid and shallow
• Sleep cycle is a form of an ultradian pattern including REM and NREM and repeats every 90 mins for 5 stages

  • (REM) - Rapid Eye Movement
  • (NREM) - Non Rapid Eye Movement
• Infradian Rhythm - Biological rhythms that occur less than once a day, eg. menstrual cycle
• Ultradian rhythms - Biological rhythms that occur more than once a day, eg. sleep stages