Alessandro Agnoli Lecture. Physical chemistry in neurology: an exciting scientific adventure.

Physical chemistry describes systems in terms of their energy and their boundary conditions. Quantitative knowledge of the future state of a system can be derived from a set of differential equations, relating to the functions defining that system, that provide reasonable estimates of its behavior. This approach, howe v e r, implies first the need to leave aside the individual characteristics of the system and, second, that the studied processes are substantially continuous and linear. Thus, it cannot be applied to whole biological systems. The cell itself is an open thermodynamic system made up of many “small molecular systems” that cooperate, working distant from the equilibrium conditions. Its existence and its functions are determined by the many interactions among its sub-systems, and it seems meaningless to seek to identify a “cause” that might be isolated and distinguished from the “effects”. The interactions show an associative character rather than an additive one, which most often implies that they are governed by non-continuous and nonlinear laws. Therefore, the behavior of such systems cannot be understood on the mere basis of additive extrapolations derived from the knowledge of each elemental process. The “reductionist” view of cellular biology, which focuses on the molecular analysis of the various components carrying out cellular functions, has created a bridge between chemicalphysicists and the biological and medical world. Indeed, chemical-physicists have, from the viewpoint of its thermodynamic and kinetic aspects,