3. Signaling system composition 1) Simple signaling pathway by an extracellular signal (1).Small effective molecules mediated signaling (called as secondary messenger) The secondary messengers are generated from (2) Signaling pathway via lager intracellular signaling molecules(proteins or enzymes) rather than secondary messenger3. Signaling system composition 1) Simple signaling pathway by an extracellular signal (1) Small effective molecules mediated signaling (called as secondary messenger) The secondary messengers are generated from (2) Signaling pathway via lager intracellular signaling molecules (proteins or enzymes) rather than secondary messenger