how human fingers actually moves - from a real hand anatomy by a professor

 professor from stanford university explains how human fingers moves.

he shows a motor mechanism like each finger having connected with 4 motor drives or pullies 

the 4 working drives are

extensor 

intrinsics 

profundus 

sublimis

if we watch the bellow video from 23rd minute we understand it better

we can use this mechanism in robotic arm it functions well like human hand