Cell receptors and cell signalling.

All cells in a multicellular organism are constantly exposed to a variety of extracellular signals that they need to interpret and translate into an appropriate response to their environment. These signals can be soluble factors generated locally (for example, synaptic transmission) or distantly (for example, hormones and growth factors), ligands on the surface of other cells, or the extracellular matrix itself. To achieve this, cells maintain a diversity of receptors on their surface that respond specifically to individual stimuli. These receptors fall into families, based primarily on the way in which they generate the intracellular signals that give rise to the particular functional responses. Moreover, the activity of a given receptor can be modulated by other signalling pathways in a variety of ways, generating the flexibility required of such a complex system. This review aims to describe the function of the major classes of receptor, including G protein coupled receptors, receptor tyrosine kinases, ligand gated ion channels, integrins, and cytokine receptors, and to demonstrate the "crosstalk" that exists between these systems.