PLSC 480, 490 and 491 all carry course credit, which means these courses are treated like any other course when it comes time to calculate distinction. For example, if you receive an A or A- on your senior essay in PLSC 480, your grade on your essay is also your grade in that class. This course then counts as one A grade toward your distinction calculations.
This is also true for PLSC 490 and PLSC 491. If you earn an A or A- in PLSC 490 and 491, which each carry one term course credit, you will receive 2 A grades toward your distinction calculations.