Question

Which part of our central neural systems acts as a master clock?

Answer 1

In forebrain part of the central neural system, just behind the anterior choroid plexus, the epithelium forms a short stalk, the pineal stalk which has a rounded body, the pineal body, at its tip. The pineal body is an endocrine gland and, therefore, secretes a hormone, named melatonin. It is also called the "sleep hormone" because it promotes sleep. Its secretion increases in dim light and decreases in bright light. Melatonin concentration in blood appears to flow a diurnal (day-night) cycle as it rises in the evening and through the night and drops to a low around noon. Because of this light-mediated response, the pineal body acts as a master clock. It may produce circadian rhythms i.e., variations following a 24 hour cycle.