eli5: Why can we bend our index finger’s first joint freely but we can’t bend our other fingers first joint(thumb excluded) without the others slightly retracting?

Question

eli5: Why can we bend our index finger’s first joint freely but we can’t bend our other fingers first joint(thumb excluded) without the others slightly retracting?

In: Biology

Answer 1

Your fingers don’t move themselves. They’re like puppets controlled by muscles in your arm. How they can move depends on where the strings (tendons) are attached. If you imagine a puppet hand (minus thumb) controlled by strings, with a glove (the skin) covering the hand and the strings, you’ll get a better sense of the limitations.