Endogenous Pacemakers & Exogenous Zeitgebers

• What regulates biological rhythms?

  Endogenous pacemakers and exogenous zeitgebers
• What are endogenous pacemakers?

  Internal biological clocks regulating rhythms
• How do endogenous pacemakers relate to the environment?

  They can be altered by environmental factors
• What is the main endogenous pacemaker?


  Suprachiasmatic nucleus (SCN)
• Where is the suprachiasmatic nucleus located?

  In the hypothalamus
• What role does the SCN play in biological rhythms?

  It controls other biological rhythms
• How does the SCN receive light information?

  From the optic nerve
• What does the SCN signal to the pineal gland?

  To increase melatonin production at night
• What is the relationship between the SCN and the pineal gland?

  • SCN sends signals to the pineal gland
  • They work together as endogenous pacemakers
  • Their activity is responsive to light
• What did Morgan (1995) study in hamsters?

  Circadian rhythms of 20 hours
• What happened when SCN neurons were transplanted into normal hamsters?

  They followed a 20-hour circadian rhythm
• What conclusion did Morgan (1995) reach about the SCN?

  It is crucial for circadian rhythms
• What are the strengths of Morgan's research?

  • Good internal validity due to controlled conditions
  • Direct observation of circadian rhythm disruption
• What did Skene & Arendt (2007) find about blind people?

  Some have normal circadian rhythms
• What is the most important exogenous zeitgeber?

  Light
• How do exogenous zeitgebers influence biological rhythms?

  They reset the biological clock
• What is melanopsin's role in the body?

  It carries light signals to the SCN
• How can humans compensate for lack of natural light?

  By using social cues like mealtimes
• What did Campbell & Murphy (1998) study involve?

  Waking participants at night with light
• What was the effect of shining light on participants' knees?

  It caused irregular sleep-wake cycles
• What limitation did Campbell & Murphy's study have?

  Small sample size of 15 participants
• What are the strengths and limitations of Campbell & Murphy's research?

  Strengths:

  • Compelling evidence of light's role
  • Validity of exogenous zeitgebers' effects

  
  

  Limitations:

  • Small sample size limits generalizability
  • Findings not replicated in subsequent studies
• Why is replication important in research?

  To check for consistency and reliability
• What does a lack of replication indicate?

  A lack of reliability in findings
• Ralph et al (1990);


  took SCN out of genetically abnormal hamsters only had a ciradian rhythmn of20 hours and transplanted them nto rats who had a 24 hour cycle. Found that the rats cyclehortened to 20 hours showing that the SCN is importannt in determinging the length of the cycle
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  What is an exogenous zeitgeber?

  an external environmental factor that resets an organism's biological clock. Exogenous zeitgebers can include: 

  • Light: The most important exogenous zeitgeber, light resets the body's clock each day to maintain a 24-hour cycle. 
  • Social cues: Meal times and work schedules can act as exogenous zeitgebers. 
  • Temperature