I don't know if they are only open for PhD students. But they were listed in my BMS program course guide as electives so I'd imagine we can get into them (maybe w/ instructor permission).
All the Fall classes I know of:
Physio I (PSL 7010)
Biochemistry (BMB 7010)
Advanced cardiovascular physio (probably requires Physio II first) (PSL 7600)
Neurophysiology (again, maybe has a prereq) (PSL 7660)
Principles of toxicology (maybe requires Pharm) (PHC 7410)
Drugs and the addictive process (PHC 6500)
General pathology (PTH 7000)
Molecular bio and genetics (MBG 7010)
Microbio (IM 7020)
Those are the ones that I have taken, am about to take, or know of people taking. There are probably more but hopefully that gives you some options for Fall classes!