Think of the body like a knit sweater. When the sweater is in good shape it moves and flows and drapes properly. Catch a snag in it, and the sweater distorts and no longer moves properly. Same with the body. Sure, the wrist muscles don't connect into the neck, but you have have muscle chains or trains (book Anatomy Trains). You also have nerves that run through, which can get adhered in tissue, so not flowing properly as you move. And there is the myofascial tissue, which can also get adhesed.
I'm not quite clear on your positioning...your elbow is bent (flexed) and when you extend your wrist (top of hand pressing towards your arm) or when you abduct (thumb moving towards your arm) you have issues that don't allow you to smoothly complete the movements. It's not typical problem positioning, so just wanting to make sure I've got you right...