Nitric Oxide Click to see full answer. Considering this, what is the first messenger in a signal transduction pathway?First messengers are the signaling molecules (hormones, neurotransmitters, and paracrine/autocrine agents) that reach the cell from the extracellular fluid and bind to their specific receptors. Second messengers are the substances that enter the cytoplasm and act within the cell to trigger a response.Additionally, what is a first messenger? Medical Definition of first messenger : an extracellular substance (as the hormone epinephrine or the neurotransmitter serotonin) that binds to a cell-surface receptor and initiates intracellular activity — compare second messenger. Also question is, what is an example of signal transduction? Epinephrine is used as a sample messenger to trigger the release of glucose from cells in the liver. The G-Protein, adenylyl cyclase, cAMP, and protein kinases are all used as illustrative examples of signal transduction.What are the 3 steps of signal transduction? Phases of Signal Transduction There are three stages in the process of cell signaling or communication: Reception-a protein at the cell surface detects chemical signals. Transduction-a change in protein stimulates other changes including signal-transduction pathways. Response-almost any cellular activity.