Muscle maps in your brain
Every time you move, the motor cortex area of your brain has to decide which movements to make. It retains a kind of 'muscle map' of your body, with most space reserved for parts that have many small muscles, such as your hands and face. The map can change if you learn a new skill requiring fine muscle control. For example, if you play a stringed instrument you may have extra space in the motor cortex devoted to the fingers.