Lesson 12 - Endogenous Pacemakers

Question 1

Endogenous Pacemakers

Answer 1

• Contains suprachiasmatic Nuclei
• Cluster of nerve cells in the hypothalamus
• SCN plays important role in generating circadian rhythms

Question 2

SCN Role

Answer 2

• Acts as a master clock linking other brain regions that control sleep and arousal, and controlling all other biological clocks throughout the body
  
  • Neurons within the SCN synchronise with each other, so their target neurons in sites elsewhere in the body receive time-coordinated signals
  • Peripheral clocks can maintain circadian rhythms, but not for long, which is why they’re controlled by the SCN
  • SCN has built in circadian rhythms, which only needs resetting when external light levels change
  • SCN receives information about light levels through the optic nerve
  • If biological clock is running slow then morning light shifts the clock to speed up
• Regulates manufacture and secretion of melatonin in the pineal gland
  
  • This is via the interconnecting neural pathway
  • SCN sends a signal to the pineal gland, directing it to increase production and secretion of the hormone melatonin at night and to decrease it as light levels increase in the morning
  • Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness.

Question 3

Folkard 1996 - Kate Aldcroft AO3

Answer 3

• Studied university student - Kate Aldcroft - who spent 25 days in a lab
• She had no access to the exogenous zeitgebers of light to reset the SCN
• At the end of the 25 days her core temperature rhythm was still at 24 hours
• Indicates that we DO NOT need the exogenous zeitgebers of light to maintain our internal biological rhythms

Question 4

Sleep-Wake Cycle AO3

Answer 4

• Extended to 30 hours, with periods of sleep as long as 16 hours
• Suggests that we DO need the exogenous zeitgebers of light to maintain our internal biological rhythms

Question 5

Light

Answer 5

• Exogenous Zeitgeber
• Receptors in the SCN are sensitive to changes in light levels during the day and use this information to synchronise the activity of the body’s organs and glands
• Light resets the internal biological clock each day - keeping it on a 24 hour cycle
• A protein in the retina of the eye called melanopsin is critical in this system

Question 6

Holidays or Night Shift

Answer 6

• Endogenous pacemakers try to impose their inbuilt rhythms of sleep (circadian rhythm)
• However this is out of sync with the exogenous zeitgebers of light
• This leads to disrupted sleep, increased anxiety and decreased alerness and vigilance

Question 7

Blind people WITH light perception AO3

Answer 7

• They have normal circadian rhythms
• Blind people WITHOUT light perception show abnormal circadian rhythms
• Shows the vital role that the exogenous zeitgeber of light levels play in maintaining our internal biological rhythms

Question 8

Burgess et al 2003 - Flight AO3

Answer 8

Found that exposure to bright light prior to an east-west flight decreased the time needed to adjust circadian rhythms to local time

Question 9

Artic Region Studies AO3

Answer 9

• Sun does not set in the summer months
• Normal sleeping patterns despite the prolonged exposure to light
• Suggests that there are occasions where the exogenous zeitgeber of light may have little bearing on our internal biological rhythms