endogenous pacemakers

• p: the importance of the SCN as an endogenous pacemaker was demonstrated in morgans study of hamsters

  E: morgan bred a strain of hamsters so that they had abnormal circadian rhythms of 20 hours rather than 24 hours. SCN neurons from these abnormal hamsters were then transplanted into the brains of normal hamsters. normal hamsters displayed the same abnormal circadian rhythm of 20 hours, showing transplanted SCN has imposed its pattern onto the recipients brains

  L: this confirms the importance of the SCN in setting circadian rhythms
• P: touitou argue that exposure to artificial light at night results in a disruption of the circadian system, which has adverse effects on health

  E: touitou's research has shown that teenagers spend increasing amounts of time on electronic media at night. the LED bulbs of these devices are enriched with a blue light component very active on the circadian clock, which leads to suppression of melatonin secretion and circadian disruption. as a result, adolescent sleep becomes irregular, shortened and delayed
• link for touitou

  L: this combination of sleep deprivation and circadian disruption is detrimental to health as shown by many studies that have found increased rates of cardiovascular disorders and mood disorders such as depression