AO1

• What are endogenous pacemakers?

  Internal body blocks that keep biological processes to time
• What are exogenous zeitgebers?

  External cues that keep internal body clocks in time (entrainment) meaning altering body clocks to match the environment
• Who found evidence that SCN is EP?

  Ralph (1990)
• What was the procedure of Ralph’s study?

  Golden hamsters with the Tau mutation compared with normal hamsters (24 hr circadian rhythm)
• What is the Tau mutation?

  Circadian rhythm of 20 hours
• What happened in Ralph’s study?

  When the SCN from normal hamsters was transplanted into the brain of Tau mutant hamsters, these hamsters gained a sleep wake cycle of 20 hours (and vice versa). This suggests the SCN is the main endogenous pacemaker in the sleep wake cycle
• What is the superchiasmatic nucleus?


  One of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms
• Where is the SCN located?

  Above the optic chasm. It receives information about light dreictly from this structure.
• The SCN passes the information on day length and light that it receives to the pineal gland.
• How does the SCN work with the pineal gland?

  Pineal gland receives information on the day length and light . It produces melatonin (a chemical that induces sleep and is inhibited during periods of wakefulness)
• Light is a key zeitgeber in humans. It can reset the SCN, thus plating a role in the maintenance of the sleep wake cycle
• Light may be detected by skin receptor sites on the body even when the same information is not received by the eyes
• Campbell found that participants were woken at various times when a. light was shone on the back of their knees. Researchers also managed to produce a deviation in the participants usual sleep/wake cycle of up to 3 hours
• Example of another exogenous zeitgeber that’s not light

  Social cues
• Research on jet lag suggests that adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms