What initiates the intracellular signaling pathways?

When a ligand binds to the receptor, it initiates a signaling pathway. One or more of these intracellular signaling proteins interact with a target protein, modifying it and influencing the cell's behavior. The alteration in the receptor triggers a sequence of signaling events. For example, the receptor might activate another signaling molecule within the cell. This in turn sets off the activation of its specific target molecule.