There is a biochemical and anatomical difference. Exhausted would implies that there is no available energy for the task at hand and enervated would suggest that the intended task lack the nervous potential to be actuated. That said, in popular discourse, there is not much difference between the two.
Systems theory has also been developed within sociology. An important figure in the sociological systems perspective as developed from GST is Walter Buckley (who from Bertalanffy's theory). Niklas Luhmann is also predominant in the literatures for sociology and systems theory.
The structuralist perspective in the social sciences is an holistic theoretical paradigm based on the Gestalt psychology principle that human behavior and experience are essentially structural in nature, that is, that they consist of individual units that researchers can isolate and study alone in order to gain a greater understanding of the whole.