The upper limb or upper extremity consists of four main parts: a girdle formed by the clavicles and scapulae, arm, hand, and forearm. Although very mobile, the limb is supported and stabilized by muscles linked to the ribs and vertebrae.
In the human body, the muscles of the upper extremity can be classified by origin, function, topography, or innervation. While a grouping by innervation reveals phylogenetic origins and embryological, the functional-topographical classification below reveals the similarity in action among muscles (with the exception of the shoulder girdle, where muscles with similar action can vary considerably in their position and orientation.
Parts of the upper limb
It has been seen that the upper limb is made up of four parts:
- Shoulder region
- Arm or brachium
- Forearm or antebrachium
- Hand or manus.
Further subdivisions of the Parts of the upper limb are given in table and fig 1.1.
1- The Shoulder region includes :
- The pectoral or breast region on the front of the chest.
- The axilla or armpit
- The scapular region on the back comprising parts around the scapula.
The bones of the shoulder girdle are the clavicle and the scapula.
Of these, only the clavicle articulates with the axial skeleton at the sternoclavicular joint. The scapula is mobile and is held in position by muscles. The clavicle and scapula articulate with each other at the acromioclavicular joint.
2- The arm ( upper arm or brachium)
extends from the shoulder to the elbow (cubitus). The bone of the arm is the humerus. Its upper end meets the scapula and forms the shoulder joint. The shoulder joint permits movements of the arm.
3- The forearm (antebrachium)
extends from the elbow to the wrist. The bones of the forearm are the radius and ulna. At their upper ends, they meet the lower end of the humerus to form the elbow joint. Their lower ends meet the carpal bones to form the wrist joint. The radius and ulna meet each other at the radioulnar joints.
The elbow joint permits movements of the forearm, namely flexion and extension. The radioulnar joints permit rotatory movements of the forearm called pronation and supination. In a mid-flexed elbow, the palm faces upwards in supination and downward in pronation. During the last movement, the radius rotates around the ulna.
4- The hand (manus) includes:
- The wrist or carpus, supported by eight carpal bones arranged in two rows.
- The proper or metacarpus, supported by five metacarpal bones.
- Five digits (thumb and four fingers). Each finger is supported by three phalanges, but the thumb has only two phalanges ( there being 14 phalanges in all).