Biological Rhythms

• What are biological rhythms?

  Patterns of change in body activity that conform to cyclical time periods
• What are circadian rhythms?

  • Biological rhythms that operate on a 24-hour cycle
  • Regulates processes such as the sleep/wake cycle and changes in body temperature
• What does circa and diem mean?


  About a day
• What is an ultradian rhythm?

  Biological rhythms that have more than one cycle in 24 hours
• What is a infradian rhythm?

  Biological rhythms that have less than one cycle in 24 hours
• What are endogenous pacemakers?


  Internal body clocks that regulate biological rhythms
• What are exogenous zeitgebers?

  External cues that influence our biological rhythms
• What do circadian rhythms regulate?

  Sleep/wake cycle, body temperature
• What is the sleep/wake cycle?

  Circadian rhythm that dictates when humans and animals sleep and wake up
• What is the primary input for the sleep wake cycle?

  Light
• What is light detected by and what does it do?


  The eyes, send a signal
• Where do the eyes send a signal to in the sleep wake cycle?

  Suprachiasmatic nucleus (SCN)
• When is human body temperature the lowest?

  36°C at 4:30 am
• When is human body temperature the highest?

  38°C 6pm
• When does sleep typically occur in relation to temperature?

  When the core temperature starts to drop and the body temperature starts to rise towards the end of the sleep cycle promoting feelings of alertness first thing in the morning
• Who did the cave study?

  Siffre
• What Siffre do?


  Spent several periods underground
• What happened in Siffre's first study?

  He immerged mid September believing it to be mid August in 1962
• How long was Siffre's second study supposed to last?

  6 months
• What happened to Siffre sleep/wake cycle?

  Changed to 25 hours but remained regular
• What does Siffre's study show?


  Sleep wake cycle was increased by the lack of external ques making him believe each day was longer that it was and in the long run believing fewer days had passed
• What did Aschoff and Wever do?

  Convinced a group of participants to spend 4 weeks in a WWII bunker deprived of natural light
• What did Aschoff and Wever find?

  All but one participant displayed a circadian rhythm between 24 and 25 hours
• What does Siffre and Aschoff and Wever's show?

  the natural sleep/wake cycle may be slightly longer than 24 hours. However, it seems humans use exogenous zeitgebers to regulate a 24-hour circadian rhythm
• What did Flokard et al do?

  • 12 people in a dark cave for 3 months Went to bed at 11:45 pm and woke up at 7:45 am
  • The researchers secretly sped up the clock "24 hour" day became 22 hour
• What did Flokard et at find?

  Only one of the participants was able to comfortably adjust to this new regime
• What did Folkard et al show?

  There is a strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers
• Strengths of circadian rhythms

  • Practical application to shift work
  • Application to pharmacokinetics
  • Support from studies
• Why is "Practical application to shift work" a strength of circadian rhythms?

  Shift workers experience adverse cognitive effects due to desynchronization of circadian rhythms, leading to concentration lapses at 6 am, increased accident risk, and increased heart disease risk. This affects productivity and workplace safety, highlighting the need for economic considerations.
• Strength of circadian rhythms -"Application to pharmacokinetics"

  
  

  • Circadian rhythms play a crucial role in determining the optimal time for drug treatments, particularly for respiratory issues.
  • The risk of heart attack is highest in early morning, allowing drugs to be taken at night and released at dusk, thereby increasing the efficacy of treatments for disorders like cancer, epilepsy, and respiratory issues.
• Why is "Support from studies" a strength of circadian rhythms?

  • Siffre study Wever and Aschoff - Folkard
  • This suggests that the body's internal clock is set 24-25 hours in the absence of external cues, and is intolerant of any major alterations to sleep and wake cycles, through processes such as shift work and jet lag
• Limitations of circadian rhythms

  • Issues with case studies
  • Poor control in studies
• Why is "Issues with case studies" a limitation of circadian rhythms?

  • Individual differences in people's natural sleep/wake cycle may be present in small sample studies by Siffre, Aschoff, Wever, and Folkard.
  • Siffre's body clock responded differently to a 48-hour cycle at 60 years old, while Czeisler's study found cycles can vary by 13-65 hours.
  • Factors like age and gender may significantly impact circadian rhythms, making it impossible to generalize results to whole populations.
• Why is "Poor control in studies" a limitation of circadian rhythms?

  In the cave studies the exposure to artificial lights such as torches was not controlled

  Research by Czeisler reveals that dim artificial lighting can adjust our circadian rhythm by 22-28 hours, despite the assumption that natural light only influences our biological rhythms. This has practical implications for the use of electronic devices like smartphones during different times of the day, as the sleep/wake cycle may vary significantly.
• What type of biological rhythm is the menstrual cycle?


  Infradian
• What is the menstrual cycle governed by?


  Monthly changes in hormone levels which regulate ovulation
• What is the menstrual cycle?


  The time between the first day of the period, when the womb lining is shed, to the day before the next period
• How long is a typical menstrual cycle?

  28 days
• What happens during the menstrual cycle?

  • The rise in levels of the hormone oestrogen cause the ovary to develop an egg and release it - ovulation
  • Then hormone progesterone helps the womb lining to grow thicker, readying the womb for pregnancy
  • If pregnancy does not occur, the egg is absorbed, the womb lining comes away and leaves the body - the menstrual flow
• Who did a study to look at synchronisation of the menstrual cycle?

  Stern and McClintock