Receptor (cell biology)
Cell surface receptors (membrane receptors, transmembrane receptors) take part in communication between the cell and the outside world. Extracellular signalling molecules (usually hormones, neurotransmitters, agonist, cytokines, growth factors or cell recognition molecules) attach to the receptor. This triggers changes in the function of the cell. The process is called signal transduction: The binding starts a chemical change on the inside of the membrane.