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.
Ecological systems theory. Ecological systems theory, also called development in context or human ecology theory, identifies five environmental systems with which an individual interacts. This theory provides the framework from which community psychologists study the relationships with individuals' contexts within communities and the wider society. Ecological systems theory was developed by Urie Bronfenbrenner. The theory is also commonly referred to as the ecological/systems framework.