. Assume the body is buried in a casket and exhumed five years later for a medical test. If the biceps brachii muscle was examined microscopically, what might can we to find and why?

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I am only guessing but I would say a shrivelled, stinky, mess!

I think the tendons will still be visible...

There are catalogues of expectation in relation to examination of exhumed corpses. These address various organs correlated to post mortem interval. PubMed might be a good place to start.

Well after five years there would only be the metabolites of the proteins that were once there (putrecsene and cadaverine, which causes the vast majority of what we call the smell of a dead body). As for the "after we die" question; physically there is only physical degradation into the basic elements that were part of our bodies(constituents). That seems to be the extent of your question... possibly a pertinent question since the physical realm is the only one we can adopt the scientific method to in order to have answers.