what are surface receptors?

Cell surface receptors, often called transmembrane receptors, are important proteins that mediate communication between the cell and the outside world. Extracellular ligands (cytokines, growth factors, hormones, neurotransmitters, or cell recognition molecules) bind to the receptor, triggering conformational changes that initiate intracellular signaling pathways (signal transduction). Cell surface receptors regulate a multitude of biological pathways required for cell growth, differentiation, proliferation, and survival.