Signal transduction

The process by which an extracellular signaling molecule activates a membrane receptor that, in turn, alters intracellular molecules, creating a response. There are two stages in this process: a signalling molecule activates a certain receptor on the cell membrane, causing a second messenger to continue the signal into the cell and elicit a physiological response. In either step, the signal can be amplified, meaning that one signalling molecule can cause many responses.