A biochemical cascade (or a signaling pathway) is a series of chemical reactions which are initiated by a stimulus (first messenger) acting on a receptor that is transduced to the cell interior through second messengers (which amplify the initial signal) and ultimately to effector molecules, resulting in a cell response to the initial stimulus. At each step of the signaling cascade, various controlling factors are involved to regulate cellular actions, responding effectively to cues about their changing internal and external environments.