How do cells recognize signals?

Cells recognize signals by means of large proteins called receptors that specifically bind the ligand or signaling molecule, triggering a response in the target cell. These receptors may be located inside or outside of the cell or embedded in the cellular membrane. Cells receive and respond to multiple signals simultaneously through their receptors. However, not all cells can recognize all signals. Only cells that have the right receptor for that specific ligand can recognize and bind to the signaling molecule.