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 social-cognitive theory is a theoretical perspective in which learning by observing others is the focus of study. Social-cognitive theory is grounded by several basic assumptions. One is that people can learn by observing others. Learners can acquire new behaviors and knowledge by simply observing a model.