It really depends on how good your undergrad notes are. Usually, your medical school course will give student enough handout to study on anyway. For instance, the Neuroscience class notes are 3 inches thick for us.
One warning about using your undergrad notes. One of my friends decided to use his undergrad class notes for Biochemistry because he *thought* his notes were more detailed and are better. But the problem is, professors tended to write test questions based on the class notes they give us. So my friend ended up studying on more material than we were required, and didn't focus his attention on the material our professor thought was important.
So I guess it will be a good idea to save your undergrad notes for reference if you encounter information on your class notes that is confusing. But generally medical school professors are friendly and very approachable, so why bother digging thru your undergrad notes when you can just go up to the prof and ask? Just my $0.02 :wink: