Melatonin:A hormone produced by pineal gland that helps regulate sleep-wake cycles. Its production increases with darkness and decreases with light exposure, under control of SCN.
Hypothalamus:A part of brain involved in many functions including hormone production, regulation of body temperature, hunger, moods etc., which also houses SCN.
Optic Chiasm: The point in the brain where the optic nerves from each eye meet and partially cross over. It's crucial for binocular vision and also transmits light information to SCN.