Have you ever wondered about the etiquette for emailing your Prof or TA? You have their email addresses on your syllabus but you might not be sure about the tone to take or what exactly to put in the email so that it sounds polite but not obsequious. 
If so, you're not alone. A couple of years ago, a blogger named Laura Portwood-Stacer wrote an excellent piece on this very topic, and more recently a UNC- Chapel Hill Professor named Anna Wortley wrote a column in the New York Times on etiquette on campus more generally. Read these and know how to mind your p's and q's.
The articles don't cover emails to TAs or to other university administrators but the general principles are good for those audiences as well. Some TAs are fine with being on a first name basis but if they haven't told you to use their first name, stay safe by using a formal title. The same goes for academic administrators like your registrar or the departmental undergraduate advisor. You are in a professional relationship with these people - write to them like professionals.
Also remember that the people you are writing have busy lives and they may not respond immediately. Unless you are facing an emergency, allow a few days for a response before following up. If you are facing an emergency, you will probably need to book an appointment to talk in person to the appropriate person.