Nearly one quarter of the motor cortex, which is the part of the brain that controls body movements, is devoted to hand and wrist movements. Your hands and wrists — or upper extremities — feature the most bones of any area of the body. A complex structure of bones, joints, ligaments, muscles and nerves, your hands and wrists are as strong as they are sensitive. As the most active part of your body, your upper extremities empower you to accomplish a number of daily tasks requiring fine motor skills, such as playing sports, typing and communicating with others.