Many enzyme-linked receptors initiate phosphorylation cascades. All act in similar manner. Proteins with SH2 Domain proteins bind to the phosphotyrosine region. MAP kinase cascades transmit many other kinds of information.
Bipolar cells activate ganglion cells ganglion cells send action potential to brain.
Tumor necrosis factor is a signaling molecule that can trigger apoptosis. Initiator caspases activate effector caspases. Effector caspases execute the cell by digesting some proteins and activating other proteins which finish off the dirty work. Sometimes TNF or fas have the opposite effect, to stimulate recovery rather apoptosis. Some converge others diverge.