Overall, the forearm comprises the lower half of the arm. It extends from the elbow joint to the hand, and it is made up of the ulna and radius bones. These two long bones form a rotational joint, allowing the forearm to turn so that the palm of the hand faces up or down. The forearm is covered by skin, which provides a sensory function. The quantity of hair on the forearm varies for different people, but typically the top features more follicles than the underside. Two large arteries run the distance of the forearm, and these are the radial and ulnar. Both blood vessels follow a course close to the bones of similar name. These vessels also branch into lesser arteries, servicing the forearm's musculature. Many of the forearm's components are innervated by the radial, ulnar, and median nerves, as well as their distal branches. On the whole, the entire arm features three long bones that are frequently broken. This is especially true for the forearm. Often, a person extends their forearm instinctually when trying to break a fall, and this ultimately leads to an arm fracture.