Receptor

Molecule allowing a cell to recognize a message and respond to it

Ligand

Molecule that specifically binds to another molecule

Cell Junctions

• Local signaling
• Use gap junctions
• Signals can bypass cell membrane

Direct 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 cell

Paracrine

• Local signaling
• Cell releases soluble signal molecules into the extracellular space
• Signals diffuse from releasing cell and reach target cell

Synaptic

• Local signaling
• Allows neurons to pass signals to other cells
• Use neurotransmitters as signal molecules

Endocrine

• 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