6.8.4 Endogenous Pacemakers and Exogenous Zeitgebers

• What are biological rhythms governed by?

  Endogenous pacemakers and exogenous zeitgebers
• Endogenous pacemakers are internal biological clocks that regulate cyclical changes in biological processes. A key example is the suprachiasmatic nucleus
• What is the most potent exogenous zeitgeber?

  Sunlight
• Endogenous pacemakers are external environmental cues.

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

  Hypothalamus
• Melatonin is a hormone produced by the pineal gland and regulated by the SCN
• Order the steps involved in the regulation of the sleep-wake cycle by the SCN:

  1️⃣ Eyes receive light signals

  2️⃣ Retinohypothalamic tract transmits signals to the SCN

  3️⃣ SCN regulates melatonin production

  4️⃣ Melatonin levels promote sleep
• What do exogenous zeitgebers help synchronize?

  Endogenous pacemakers
• Endogenous pacemakers ensure that rhythms are maintained even in the absence of external cues.
• The SCN receives light signals from the eyes via the retinohypothalamic tract
• What suppresses the release of melatonin?

  Light
• Sunlight is the most significant exogenous zeitgeber.
• Match the feature with the correct regulator of biological rhythms:

  Originates from internal biological clocks ↔️ Endogenous pacemakers

  Originates from external environmental cues ↔️ Exogenous zeitgebers

  Master clock for sleep-wake cycle ↔️ SCN

  Most significant zeitgeber ↔️ Sunlight