Receptor: A receptor is a protein on the surface of a cell that binds to specific signal molecules, allowing the cell to respond to those signals.
Signal Transduction: Signal transduction is the process by which an extracellular signal is converted into an intracellular response. It involves a series of molecular events that amplify and transmit the signal within the cell.
Second Messenger: Second messengers are small molecules inside cells that relay signals from receptors on the cell surface to target molecules within the cell, amplifying and diversifying the initial signal.