circadian rhythm

• how long is a circadian rhythm?

  a day
• name the main circadian rhythm in humans

  sleep-wake cycle
• describe the concept of "body clocks" and how they are regulated

  • regulate circadian rhythm
  • body clock = suprachiasmatic nucleus, found in hypothalamus
  • this pacemaker reset so body is in synchrony with outside world
  • light sets the body clock to the correct time in a process called photoentrainment
  • light sensitive cells send messages about direct light directly to the SCN
  • sleep wake cycle subject to this entrainment process
• in what two time periods do our strongest sleep drives occur?

  • 2-4am
  • 1-3pm
  • sleep experienced between these periods less intense if we've had sufficient sleep, more intense if we haven't
• apart from the circadian rhythm, what are sleep and wakefulness controlled by?

  Homeostatic processes
• How does homeostasis control sleep and wakefulness?

  • when we have been awake for a long time, homeostasis will tell us that the need for sleep is increasing
  • Because of the amount of energy used up during when we are awake
  • Homeostatic drive for sleep increases gradually throughout the day
• What does the term "free running" mean in relation to the circadian rhythm?

  Internal circadian clock will maintain a rhythm of 24-25 hours even in the absence of external cues
• What can affect/shift a circadian rhythm?

  Major altercations in sleep, as this causes the biological clock/SCN to be completely out of balance
• Describe a case study providing evidence for circadian rhythms

  Siffre-

  • subjected himself to long periods within caves with no external cues to guide his rhythms
  • Therefore only thing that influenced his behaviour was his internal biological clock
  • Spent 61 days underground, resurfaced thinking it was September when it was really August
  • Second occasion- spent six months in a cave and his circadian rhythm settled to over 24 hours
  • found that his body clock ticked slower when he became older
• evaluation of circadian rhythms?

  • 😊 importance of light- Hughes- hormone release in ppl at British Antarctic Station. Normally, cortisol levels rise at waking at fall at sleep. Spent three months in darkness, cortisol levels only rose at noon instead of at dawn. Daylight varies circadian hormone release
  • ☹️ individual diffs- circadian rhythms vary from 13-65 hrs
  • 😊 Siffre- free running studies
  • ☹️ temp more important that light- Buhr et al- small changes in body temp sends powerful signals to body clock- sets timing of cells, causes tissue to become active/inactive