The Upper Arm
THERE IS ONLY ONE BONE IN THE UPPER ARM, THE Humerus. This powerful, long bone has two articulated ends with its upper end forming a joint with the Scapula. This joint is important in that it is the origin of all movement in the arm and has thus been tailored in such a way as to allow maximum movement. Movement is made possible by the shallow socket of the Scapula, and the head of the Humerus, which is approximately one third of a sphere, being connected.
The lower end of the Humerus has two articulated areas. The first fits into a socket on the Radius (one of the two bones of the lower arm), the other forms a joint with the second bone of the lower arm, the Ulna. These two articulations of the lower Humerus can be easily seen and felt as they are usually very pronounced.
The three main muscles of the upper arm are the Deltoid, the Biceps and the Triceps. Other muscles include the Brachialis and the Corobrachialis. The Deltoid is attached to the Clavicle, the Scapula and Acromion, connecting it to the body. It inserts into the Humerus of the Deltoid tuberosity (see page 26) and is divided into three parts which all perform distinct functions. The first controls the flexion of the arm, the second the extension and the third the raising of the arm.
THE BICEPS PULLS THE FOREARM TOWARDS THE SHOULDER DURING contraction and has tremendous potential for a relatively small muscle when strengthened. At its origin the Biceps muscle is split into two heads of strong tendon. One of these tendinous heads is attached to the Scapula, the other (the shorter of the two) is attached to the Corocoid Process. The insertion of the Biceps is at the Radius of the lower arm. This insertion is what allows the lever action of the arm as the Biceps pulls the forearm towards the shoulder during contraction.
The Triceps muscle runs along the underside of the upper arm. The Triceps has three tendinous heads at its origin (long, medial and lateral). The long head attaches to the lower section of the Scapula. The medial and lateral heads both attach to the underside surface of the Humerus. The insertion of the Triceps muscle spans from around the middle of the Humerus right up to the upper region of the olecranon at the elbow.
Lying underneath the Biceps muscle and adding its bulge in both flexion and contraction is the Brachialis. With its origin along the shaft of the Humerus and its insertion into the Ulna, the Brachialis performs a similar function to the Biceps and works in unison with it.
There are four smaller muscles with their origin along the Scapula and connecting to the upper part of the Humerus: the Supraspinatus, the Infraspinatus, the Teres Major and the Terse Minor. Running underneath the Deltoid, the lower Trapezius and the upper Latissimus Dorsi, these muscles help operate the rotation and backward and forward movement of the shoulder and upper arm. These muscles can affect the surface as well by causing an extra bulge in the Deltoid and Latissimus Dorsi depending on the movement and pressure placed on the arm and shoulder.
