Requirements for letters of recommendation are highly individualized for each medical school. Take a look at the websites of the schools you are interested in to gauge what they require for letters of rec!
A common, but definitely not universal, requirement is to have 3 letters from people who have taught you in a class setting in college, 2 of which in a science subject, 1 more from any subject. There are plenty of medical schools that also require a letters from people other than professors, though, so keep your options open.
In addition, these two links to previous questions on our Q&A may provide even more information about obtaining letters of rec specifically at Michigan.
Feel free to stop by our advising hours if you have any more questions you’d like to discuss in person!
-Owen, PMH Advisor