[intracellular signal transmission].

Information is received by cells at their exterior surface in forms of hormones, growth factors, neurotransmitters, antigens and other signalling molecules. Their information must be transduced through binding to membrane receptors, so as to elicit the appropriate biological response from the manifold repertoire of a cell. The machinery used by a cell to translate the signal from exterior membrane-interactive ligands to the inside of the cells and to generate second messengers is the topic of this essay.