second messenger

A second messenger is a small molecule inside cells that helps transmit signals from the outside to the inside of the cell. When the body receives a signal, like a hormone or neurotransmitter, it first binds to a receptor on the cell surface. This triggers the release or production of second messengers, which then activate other parts of the cell to cause a response, such as changing gene activity or releasing substances. Think of second messengers as internal communication messengers that help coordinate cellular actions efficiently in response to external signals.