Research topic sub divisions

My Research topic is to be a Nurse Practitioner we are supposed to break it down into seven subcategories but I was unable to really come with seven but I did find all types of different specialty fields that there for Nurse Practitioners.  These consists of areas such as Pediatrics,  Neonatal Nursing, Adult nursing, psychiatric nursing, etc.  The history of Nurses. To find out how where it all began and how long it has been in existence. This is all could come up with.  I really tried but I couldn't think of anything else so here's what i have.