First the receptor who gets a signal that there is a need in the organism, then it's the control, who gets the message and interprets it, then the effector who puts the plan in action, an example of this is when you get a cut, the receptor sees that that area is losing blood, so it sends a message to the control center aka the brain, who sends a message to they effector that deposits the resource needed (blood) to the area that lost it. Hope I helped