Shoulder - bark / ramię

Dictionaries give the translation of shoulder for both bark and ramię.  So, what is the difference between bark and ramię?  Here's what I have found from asking around and reading up.

I believe ramię refers to the upper arm, including the deltoid muscle.  Bark describes the broader area of the shoulder.  I believe it can describe the deltoid area of the upper arm, the trapezius area, (from the base of the neck outwards) and the shoulder blade collectively or individually.

Both words can be used to describe the same area of the upper arm.  Someone, regarding their flu or covid vaccination, would say that the location of their jab was ramię but if hit hurts later, they may say:

Boli mnie bark po szczepieniu.

Szczepieniu is the locative form of szczepienie - vaccination.