Biological rhythms

• Biological rhythms exert an important influence on the way in which body systems behave. They are cyclical in their pattern.

  • They are influenced by both endogenous pacemakers and exogenous zeitgebers.
• Endogenous Pacemakers: These are internal biological clocks, such as the suprachiasmatic nucleus (SCN) in the hypothalamus, which regulate rhythms like the sleep-wake cycle.
• Exogenous Zeitgebers: These are external environmental cues, such as light, temperature, or social cues, that influence and entrain our biological rhythms to align with the environment.
• Ralph et al. (1990) conducted a study on biological rhythms to investigate the role of the suprachiasmatic nucleus (SCN).

  • Procedure: Ralph and his team used mutant hamsters with a naturally shorter circadian rhythm of around 20 hours. They then transplanted the SCN from these hamsters into normal hamsters with a 24-hour circadian rhythm.
  • Findings: The recipient hamsters adopted the 20-hour rhythm, indicating that the circadian rhythm was controlled by the SCN.
• Campbell and Murphy (1998) investigated the role of light as an exogenous zeitgeber in regulating the sleep-wake cycle.

  • Procedure: Participants were exposed to light on the back of their knees during the night, bypassing their eyes.
  • Findings: This exposure shifted their circadian rhythms by up to 3 hours, demonstrating that light can influence biological rhythms through pathways other than the eyes.