One thing I left out in my response was about fixators. Basically, fixators are a type of synergist, that prevents movement at another joint. This allows for maximum movement of the main muscle. Basically at elbow flexion, the muscles of the scapula help keep it still due to the fixators (Martini and Nath 2009 p. 340). This allows for flexion to be isolated to the elbow.
You mentioned two types of movement that I wasn't as familiar with: "Retraction- Movement at your arms to your shoulders". Here I picture a superman pose. Retrusion- is opposite of Protrusion, moving your part posteriorly, here I picture superman trying to fly in reverse.
I learned a lot just from reading your assignment.
Martini, R., Nath, J. (2009). Fundamentals of Anatomy and Physiology. (8th ed.). San Francisco, CA. Pearson Education Inc.