Generalisation in databases
First of all, if this is homework, please tag it as such.

Secondly if it's not homework and you're doing this in a professional environment, get a professional to do it (or at least to thoroughly scrutinize your final design). Schema design underpins your application design, and flows on from clarity in business requirements and how well you understand those requirements. If you don't completely and clearly understand the requirements, your schema is going to be miles off the mark.

And, to actually answer the question (at least as best I can with the information given), I'd keep the staff in one table, however you may want to create ancillary tables for each 'type' of staff member (doctor, nurse, janitor, admin, etc) to store data specific to that staff-member-type. To give an answer that's any more specific, the requirements need to be more specific.