Signaling pathways translate extracellular and intracellular cues into diverse cellular responses. The output of a pathway may vary in its intensity and time of response, depending on the cell’s requirements. Some signaling pathways generate a gradually increasing cellular response as the concentration of signaling molecules increases; the higher the concentration of signaling molecules, the stronger the cellular response. On the other hand, some signaling pathways are activated like an on-off switch when the number of signaling molecules is above a certain threshold concentration. Some cellular processes, such as neurotransmission, need a swift response within milliseconds after receiving a signal. Cells may achieve this with ion concentration changes and protein modifications, such as phosphorylation, that are easily reversible. In contrast, certain processes, such as cell differentiation, require a prolonged response spanning hours or days. For instance, signaling pathways must continuously induce transcription and translation during embryonic development to regulate cell fate decisions.