Biological Rhythms

• Circadian rhythms.


  Have cycles that generally occur once every 24hrs.

  
• Infradian rhythms


  Have cycles that occur less than once every day.

  
• Ultradian rhythms


  Have cycles that occur more than once every 24 hours.

  
• Biological rhythm


  Distinct patterns of changes in biological activity that conform to cyclical time periods.

  
• Siffre study


  spent extended periods underground. Deprived of exposure to natural light and sound, but with access to adequate food and drink. His biological rhythm settled down to one that was just beyond the usual 24 hours.

  
• Aschoff and Wever


  Participants spent 4 weeks in a WWII bunker deprived of natural light. All but one of the participants displayed a circadian rhythm between 24 and 25 hours.

  
• Folkard et al.


  12 people lived in a cave. Researchers sped up the clock so a 24-hour day lasted 22 hours. No participants were able to adjust to the new regime.

  
• The sleep/wake cycle


  The fact that we feel drowsy when it's night-time and alert during the day demonstrates the affect of daylight - an important exogenous zeitgber - on our sleep/wake cycle.

  
• Exogenous zeitgebers


  External cues in the environment that entrain our endogenous rhythms.

  
• Endogenous pacemakers


  Internal body clocks that regulate many of our biological rhythms.

  
• Seasonal affective disorder - SAD


  Depression associated with seasonal changes, usually the onset of winter and decreased darkness.

  
• Stages of sleep


  90-minute cycles during sleep brain, sleep escalator from stage 1 to 5 and REM. Brain wave activity changes.

  
• What happens in stage 1 of sleep?


  Light sleep; person can be easily woken. Theta waves in stage 1; person in light sleep and can easily be woken.

  
• What happens in stage 2 of sleep?


  Sleep spindles, theta waves and mixed EEG activity. Light sleep where person can be easily woken.

  
• What waves are present in stage 3 and 4 of sleep?


  Involves delta waves that are slower and greater amplitude than earlier wave patterns. This is deep sleep/slow wave sleep and it's difficult to rouse somebody at this point.
• Rapid eye movement (REM sleep)


  A kind of sleep that occurs at intervals during the night and is characterised by rapid eye movements, more dreaming and bodily movement, and faster pulse and breathing.

  
• Exogenous cues for circadian rhythms.


  Day light. Social cues - meal times, bed times ect.

  
• Examples of a circadian rhythm.


  Sleep/wake cycle and body temperature.

  
• Exogenous cues for infradian rhythms.


  Pheromones and light.

  
• Suprachiasmatic nucleus (SCN)


  .Tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain where the optic nerves from each eye cross. The primary endogenous pacemaker in mammals. Receives info directly from this structure.

  
• Melatonin


  Produced by pineal gland at night, governs sleep/wake cycle. Production inhibited during periods of wakefulness.

  
• Light

  A zeitgeber in humans that can reset the main endogenous pacemaker (SCN) and plays a role in the sleep/wake cycle.

  
• Social cues entraining circadian rhythms.


  Schedules created by others, e.g. mealtimes and bedtimes. Circadian rhythms start at 6 weeks. Most babies entrained by 16 weeks. Schedules imposed by parents are a key influence. Adapting to local eating and sleeping times is an effective way of entraining circadian rhythms and beating jet lag.

  
• Zeitgebers


  External factors in the environment that reset our biological clocks through a process called entrainment.

  
• Light as an exogenous zeitgeber.


  One of the most dominant EZs; resets body's pacemaker through SCN. May explain why Campell and Murphy found that shining lights on knees caused a shift in circadian rhythm.

  
• What are Circadian Rhythms (CR)?


  - Pattern of behaviour that occurs approximately every 24 hours, set and rest by environmental light levels
• examples of Circadian Rhythms


  - Sleep-wake Cycle:

  - Hormone Production:
• What are Ultradian Rhythms?


  - Cycles that last less than 24 hours e.g. sleep cycle which repeats every 90-100 minutes
• What are Infradian Rhythms?


  - Have duration greater than 24 hours, may last days, weeks, months or years
• What are Endogenous Pacemakers?


  - Mechanisms within body that govern internal, biological bodily rhythm
• What is the Suprachiasmatic Nucleus (SCN)?


  - Main endogenous pacemaker, lies in hypothalamus
• What is the Pineal Gland?


  - Produces and secretes melatonin at night and decreases release as light levels increase
• What are Exogenous Zeitgebers?


  - Environmental cue helping regulate biological clock