The pronator teres muscle is located on the palmar side of the forearm, below the elbow. Aided by the pronator quadratus, its function is to rotate the forearm palm-down. This is also known as pronation. The pronator teres muscle has two heads: the humeral head and the ulnar head. As the names imply, they connect the ends of the humerus and the ulna to the radius. The humeral head is the larger and shallower of the two. It begins above the medial epicondyle, on the medial supracondylar ridge and the common flexor tendon. The ulnar head originates below the elbow on the inside of the coronoid process of the ulna. The two heads come together, cross the forearm diagonally, and insert halfway down the lateral surface of the radius via a tendon. The pronator teres is innervated by the median nerve. Pronator teres syndrome is sometimes attributed to neurogenic pain in the wrist. It is caused by overactivity of the pronator teres muscle in which the median nerve becomes entrapped. Repetitive throwing or turning of a screwdriver can cause pronator teres syndrome.