ABSTRACT
To coordinate the function of metazoan life forms for mutual, organismal benefit, the cells of the organism must communicate. In simple multicellular organisms, electrical coupling, cell-contact events, and the local diffusion of metabolic and messenger molecules are sufficient. Neighboring cells are informed by mass action, allosteric enzyme interactions, or specific binding to receptors. In a larger organism with a circulatory system, coordinating messages in the form of small molecules may flow through the organism to arrive at tissues possessing specific receptors, with complex postreceptor events. Also, neural fibers arborize across great distances to release communicating molecules to specialized receptors when triggered by propagated depolarization of the neuronal membrane (1).
