What Causes Jitters In Fingers When Trying To Fold Them?

When I spread my fingers or if I try to extend my fingers, they jitter. If I put my hand in a relaxed position the movement stops. It s not violent or late movements, but fine little constant movement, they tend to go side to side, but not back in forth like in a clasping motion. I m a little nervous, if only because I can t find anything on the internet that describes my symptoms, and the anxiety (I can t imagine) is helping the situation. Also the slower the movement, the worst the jitters, while if I move my fingers at normal speed the twitter is virtually non-existent. Is this just physiological? Any advice would be incredibly helpful.