Circadian Rhythms

• Circadian Rhythm:

  • type of biological rhythm (approx 24 hours)
  • regulates a number of body processes e.g. sleep-wake + changes in core body temp
• Sleep-Wake Cycle:

  • humans/animals will sleep or wake according to this cycle
  • this is dependent on the amount of light (an exogenous zeitgeber) they are exposed to
• Suprachiasmatic Nuclei (SCN):

  • found in the hypothalamus
  • detects the level of light present and uses that info to coordinate the activity of the entire circadian system
• Melatonin:

  • plays a role in 'triggering' sleep by responding to a decrease in light levels
• Desynchronisation (Shift Work):

  • if an individual starts working night shifts they will feel sleepy
  • this is because their EPs will want them to sleep because it takes a few days for our circadian rhythms to adjust
  • Similarly, they will find it hard to sleep during the day because their EPs will want them to be more active - pineal gland wont produce melatonin
• Desynchronisation (Jet Lag):

  • if an individual arrives in NY at 9pm from LDN you have gained time and your EPs will be preparing you for sleep - as your brain thinks its the middle of the night - so you will be sleepy/ groggy -> makes it difficult to sleep later
• Pineal Gland:

  • contains light-sensitive cells
  • when light is sensed melatonin production increases
  • this induces sleep by inhibiting brain mechanisms that promote the awake state
• Melatonin Production:

  low levels of light (retina) --> melanospin carries signals to SCN --> axon pathway to pineal gland --> melatonin--> induced sleep