A01

• The suprachiasmatic nucleus (SCN) is an endogenous pacemaker, responsible for maintaining circadian rhythms. It is located in the hypothalamus and receives light information from the optic chiasm. During the day, the SCN passes light information to the pineal gland which inhibits melatonin production, a hormone which induces sleep. At night, melatonin production increases.
• DeCoursey showed the importance of our SCN by destroying it inside the brains of 30 chipmunks and returning them to their natural habitats. This greatly impacted their sleep/wake cycle as many of them were killed by predators. Most likely because they were awake when they were supposed to be asleep and thus more vulnerable to predators.
• Exogenous zeitgebers are external factors in the environment that reset (entrain) our biological clocks, such as light and social cues. Research has demonstrated that light can be detected by skin receptors and affect our sleep/wake cycle even when that information isn’t taken up by the eyes. Social cues, such as mealtimes and bedtimes, start influencing a baby's sleep/wake cycle around 16 weeks. Adapting to local sleep and bedtimes is an effective way of entraining your circadian rhythm and beating jet lag.