Communication by Extracellular signals usually involves six steps: (1) synthesis and (2) release of the Signaling molecule by the signaling cell; (3) transport of the Signal to the target cell; (4) detection of the signal by a specific receptor protein; (5) a change in cellular metabolism, function, or development triggered by the receptor-signal complex; and (6) removal of the signal, which often terminates the cellular response.  Subscribe in a reader