Models of motivation have been traditionally classified along the lines of homeostatic/priming dichotomies using a diversity of definitions and names. Here, similar classification is used to describe a model of behaviour made of two well-defined mechanisms connected in series representing priming and homeostasis, and comparisons with well-known concepts in the field of animal behaviour are presented in order to show the advantages of this model in interpreting some problematical areas of animal motivation. The resulting model is analyzed as a Volterra nonlinear system and a simulation example is explained.