with high pulls you dont pull the bar upward with your arms at all. It's the explosive power from hip and ankle extension and the shrug that throws the bar up. The arms stay locked and stiff until after the top of the "jump" when you have shrugged, then you let your elbows bend. However, you dont pull along with the arms, the elbows just bent so you can pull the bar higher while holding it close to your body.
And remember: Don't get so caught up in the muscles these exercises work, the movement is more improtant. You develop power in the tripple extension of the kne, hip and ankle. Something that is very important in most sports.