final

• Zeitgebers: stimuli that help establish and maintain biorhythms
• the sun is the most important zeitgeber
• larks = morning people
• night owls = most adolescents
• larks (stability) have low neuroticism, high agreeableness, and high conscientiousness
• night owls (plasticity) have more openness and extraversion
• the same differences in serotonergic functioning that are hypothesized to contribute to personality stability may be responsible for morningness
• teens reflect changes in melatonin release (pineal gland)

  • after teen years, people tend to stop being night owls
  • might indicate brain maturity
• night shifts interfere with circadian rhythm

  • 5-10% of night workers
• jet lag is worse when traveling east
• daylight savings

  • phase advance in fall 1 hour (west)
  • phase delay in spring 1 hour (east)
• daylight savings time correlates with more heart attacks since sleep deprivation leads to inflammation and sympathetic activation
• the body's master clock is the suprachiasmatic nucleus (SCN)
• the SCN has per, tim, and clock proteins
• the SCN is above the optic chiasm (supra)
• SCN receives information from special cells in the retina called intrinsically photosensitive retinal ganglion cells (ipRGC)
• ipRGC

  • no visual image processing
  • contains photopigment called melanopsin
  • contributes to pupil light reflex
• the photopigment melanopsin chemically changes in response to light
• SCN is only active during the day and helps distinguish between day and night
• SCN --> SNS --> pineal gland
• melatonin does not keep you asleep, it only helps initiate it
• low SCN activity --> low sympathetic activity --> pineal activity rises, more melatonin
• SCN can generate and maintain rhythms independently

  • isolated SCN tissue shows cycle
  • SCN transplantation shows original cycle
• peripheral clocks exist but SCN is quicker
• SCN adjusted after 1-2 cycles, lungs 6 cycles, and liver 16 cycles in rats
• peripheral clocks are more strongly influenced by daily feeding cycles
• SCN receives light from retina but still maintains own timekeeping mechanisms
• per (period) gene, tim (time) gene, clock gene produce proteins
• if high tim and per, low clock
• if low tim and per, high clock
• clock protein - circadian locomotor output cycles kaput
• the 24 hour production and degradation of specific proteins enables SCN to tell time
• clock increases tim and per
• pineal gland dependent on SCN for circadian rhythms
• melatonin diffuses into CSF of 3rd ventricle
• melatonin suppressed by light, peaks at 4am
• taking too much melatonin can lead to sleepiness during the day
• pineal gland can disrupt hormones (testosterone and estrogen) and can interact with other medications, thinning blood
• cortisol released by adrenal gland, promotes arousal
• cortisol is highest in the early morning and remains in the blood for 3 hours