The arm supports the hand, which is the main way you manipulate your environment. There are three main bones of the arm: the humerus in the upper arm, and the radius and ulna in the forearm. The shoulder is where the humerus joins the torso; the elbow is the joint between the humerus, ulna and radius; and the wrist is the joint between the radius and carpal bones. There are many muscle attachments of the arm that control the shoulder, elbow and wrist.
The Humerus
The humerus is the bone of the upper arm. It articulates (forms a joint) with the glenoid fossa of the scapula at the shoulder and the radius and ulna at the elbow.
The shoulder muscles that attach to the humerus are the deltoid, suprasinatus, proctoralis major, teres major, lattisimus dorsi, infraspinatus, teres minor and subscapularis. The muscles of the forearm that attach to the humerus are the brachialis, coracobrachialis, brachioradialis, triceps brachii and anconeus. The biceps brachii atttachs to both the shoulder and forearm.
The gleno-humeral joint at the shoulder is a shallow ball and socket type joint; the ulna and radius join the humerus in a combination hinge and pivot joint that allows for stability of the elbow and rotation of the forearm.
The Ulna
The ulna is a long bone of the forearm that articulates with the humerus and radius. The ulna is largest at the elbow and forms a hinge joint with the humerus. The ulna and radius are joined to the radius at the elbow by a pivot joint and by a sheet of connective tissue that allows the forearm to rotate the hand in both prone and supine orientations.
The muscles attached to the ulna include the brachialis, triceps brachii and anconeus of the elbow; the extensor group of the hand and wrist including the extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis muscles; the flexor group including the flexor carpi ulnaris, flexor digitorum superficialis and profundus muscles; and the pronator and supinator muscles of the forearm including the pronator quadratus, pronator teres and supinator muscles.
The Radius
The radius is the other long bone of the forearm. It articulates with the humerus at the elbow, the ulna along the forearm, and the scaphoid and lunate bones of the wrist. The radius is larger at the wrist end and provides much of the stability of this joint with its condyloid-type joint and is small at the elbow where it forms a pivot joint.
The muscles that attach to the radius include the biceps brachii of the upper arm; the supinator, pronator teres and pronator quadratus of the forearm; and the flexor digitorum superficialis, flexor pollicis longus and extensor pollicis muscles of the hand.
References
- "Gray's Anatomy: The Anatomical Basis of Clinical Practice"; Susan Standring (Editor); 2008
- "Trail guide to the body: how to locate muscles, bones and more"; Andrew Biel; 2005
