Management tends to confuse these two words (the reality is that we all tend to confuse the two). Motivation comes from outside, such as the need to earn money. The management approach to motivation is typically the "carrot or the stick" - - viewing your life and career as a production line. Inspiration is about finding meaning in your work - - what is your purpose and what really inspires you. What drives your enthusiasm? Inspiration involves playing to your strengths and passions. Motivation is more sprint than marathon - - it may or may not have the earnestness of inspiration.
I would recommend thinking about inspiration in the context of the linkage between what you do and the impact you have.