Receptors are expressed in all types of cell membranes. Cell surface receptors are typically transmembrane proteins because they bind signal molecules in the extracellular space and generate different intracellular signals on the opposite side of the plasma membrane.
There are 3 major categories of PM receptors:
(1) Neurotransmitter-activated receptors which include 2 classes:
(i) G-protein coupled receptors (GPCRs);
(ii) ligand-gated ion channels.
(2) tyrosine kinase receptors (see outline)
(3) Nuclear/hormone/steroid receptors