W/ Melatonin

• 1. eyes detect light and send message to SCN to indicate day or night
  2. if no light, SCN sends signal to pineal gland to release melatonin; increase drowsiness and decrease cell activity
  3. if light, SCN sends inhibitory signal to pineal glad; inhibition of melatonin release
• Light cues cycle 24 hours; circadian rythm can undergo daily resetting; keeps persons sleep-wake cycle aligned to 24 hours