CELLULAR COMMUNICATIONReceptor Molecule allowing a cell to recognize a message and respond to itLigand Molecule that specifically binds to another moleculeCell Junctions • Local signaling • Use gap junctions • Signals can bypass cell membraneDirect Contact • Local signaling • Requires cell to cell contact • Signal molecule bound on cell membrane • Signal molecule on one cell binds to receptor molecule on another cellParacrine • Local signaling • Cell releases soluble signal molecules into the extracellular space • Signals diffuse from releasing cell and reach target cellSynaptic • Local signaling • Allows neurons to pass signals to other cells • Use neurotransmitters as signal moleculesEndocrine • Long distance signaling • Signals travel through blood vessels before reaching target cell • Insulin released by pancreas into bloodstream causes cells all over the body to absorb glucose from the bloodstream