melatonin and circadian rhythm regulation. brain with pineal gland

melatonin circadian rhythm regulation brain pineal gland suprachiasmatic nucleus sleepwake cycle human anatomy vector eye sunlight production hormones wakefulness light sensitivity endocrine system hypothalamus anatomical poster hormone flat neuroendocrine glandular secretion sleep serotonin synthesis biological timekeeping neurotransmitter photoreceptor cells nuclei scn entrainment jet lag disorder clock retina optic nerve insomnia clinical pharmacology regulation nucleus sleep-wake cycle anatomy