A01

• What are endogenous pacemakers?

  Mechanisms within the body that govern the internal, biological bodily rhythms
• What are exogenous zeitgebers?

  An environmental cue that helps to regulate the biological clock in an organism
• What are two examples of endogenous pacemakers?

  1. The suprachiasmatic nucleus (SCN)

  2. The pineal gland
• What are two examples of exogenous zeitgebers?

  1. Light

  2. Social cues
• What is entrainment?

  When our biological-clock is reset each day by cues in the environment (e.g. the light cues of sunrise and sunset)
• State 2 studies which show support for the role of the SCN (endogenous pacemakers) on our circadian rhythms

  1. Morgan (1995) = hamsters

  2. DeCoursey et al. (2000) = chipmunks
• What study shows support for the role of light (exogenous zeitgeber) on our circadian rhythm?

  Campbell and Murphy (1998) = light exposure to back of knee
• What study shows support for the role of social cues (exogenous zeitgeber) on our circadian rhythm?

  Klein and Wegmann (1974) = jetlag
• What is a practical application of research into circadian rhythms?

  Shift workers and jetlag
• What is an issue with using animal studies?

  Makes it difficult to generalise onto humans as animals' brains work very differently to ours
• What is the pineal gland?

  • The SCN also regulates the manufacture and secretion of melatonin in the pineal gland
  • Melatonin induces sleep in the body
  • The pineal gland is a pea-like structure in the brain just behind the hypothalamus
  • The SCN sends signals to the pineal gland directing it to either increase or decrease the levels of melatonin in the body
  • At night time it will tell the pineal gland to increase the production and secretion of melatonin, whereas in the morning, as light levels increase the production and secretion of melatonin by the pineal gland will decrease
• What is the SCN?

  • The suprachiasmatic nucleus (SCN) is a tiny cluster of nerve cells located in the hypothalamus in the brain
  • It acts as the main endogenous pacemaker, regulating the body's circadian rhythms, such as the sleep-wake cycle
  • The SCN receives information about light from the eyes via the optic chiasm, even when the eyes are closed, helping to synchronise the internal body clock with the external environment
  • Acts as the master internal body clock
  • Affects other bodily functions such as body temperature, hormone release (e.g., melatonin via the pineal gland) and sleep-wake patterns