Melatonin, known chemically as N-acetyl-5-methoxytryptamine, is a hormone produced in the pineal gland located in the brain. The pineal gland is an endocrine gland and is responsible for the production and distribution of melatonin in the human body.
The production of melatonin helps regulate the sleep-wake cycle and is responsible for the entrainment of the circadian rhythm in humans and animals. What this means is that it helps to generate sleep at the appropriate time, namely as a result of lower light levels.
How melatonin works
The pineal gland secretes melatonin at varying rates during the day and night. Melatonin receptors in the body receive this hormone as it is released from the pineal gland and into the bloodstream.
Levels of both light and dark are received by the retinal photosensitive ganglion cells in the eyes. These cells are different from the primary image receptors of rods and cones and make up only about 2% of the retinal ganglion.
These photosensitive receptors are then responsible for delivering information to the brain about the levels of light and darkness found in the external environment. These neural signals are then associated with the production of the specific hormone melatonin.