The upper limb and lower limbs were evolved basically for bearing the weight of the body and for locomotion. In quadrupeds forelimbs and hindlimbs are, therefore, built on the same basic pattern.
Each limb is made up of a basal segment or girdle, and a free part divided into proximal, middle and distal segments. The girdle attaches the limb to the axial skeleton. The distal segment carries the five digits.
The following table will elicit the similarity between two limbs
However, with the evolution of the erect posture in man, the function of weight-bearing was taken over entirely by the lower limbs. As a result of this, the upper limbs and hands became free and gradually evolved into organs having great manipulative skill. This has become possible because of a wide range of mobility at the shoulder. The whole upper limb works as a jointed lever.
The human hand is a grasping tool. It is exquisitely adaptable to perform various complex functions.
The upper limb has been highly modified in humans to enable the superior reach and grasp.
Parts of the Upper Limb
The upper limb can be divided into following parts
- Shoulder Region
- Arm (or brachium)
- Forearm (or antebrachium)
- Hand (or manus).
Shoulder region consists of the following
- 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.
Also called upper arm or brachium, the arm extends from the shoulder to the elbow (or cubitus). The bone of the arm is the humerus. Its upper end meets the scapula and from the shoulder joint. The shoulder joint permits movements of the arm.
Forearm or Antebrachium
Forearm extends from the elbow to the wrist. The bones of the forearm are the radius and the 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 elbow joint permits movements of the forearm, namely flexion, and extension. The radioulnar joints permit rotatory movements of the forearm called pronation and supination.
- The wrist or carpus
- The hand proper or metacarpus
- Five digits
The carpal bones form the wrist joint with the radius, intercarpal joints with one another, and carpometacarpal joints with the metacarpals. The phalanges form metacarpophalangeal joints with the metacarpals, and interphalangeal joints with one another. Movements of the hand are permitted chiefly at the wrist joint. The thumb moves at the first carpometacarpal joint and each finger at its metacarpophalangeal joint.
Bones of Upper Limb
Clavicle is the bone that connects the shoulder girdle to the thorax. On one side it articulates with sternum at sternoclavicular joint and on the other side, it articulates with the acromion process of the scapula at acromioclavicular joint
Scapula has a complex anatomy and is responsible for providing overhead movements to the human shoulder. It articulates with clavicle on one side. On the other side it also articulates with the shoulder through its glenoid cavity, a cavity that forms a joint with the head of humerus called shoulder joint or scapulo-humeral joint). It also has a gliding motion with thorax at its inner surface. This gliding action adds to the mobility of shoulder joint.
The arm is formed by a single bone called humerus. On upper end, it forms shoulder joint and lower end it forms elbow joint by articulation with the ulna.
Forearm contains two bones-radius and ulna. Ulna forms elbow joint with the lower end of humerus. Radius and ulna articulate with each other at superior and inferior radio-ulnar joints. These joints allow movements of pronation and supination.
Wrist or carpus is formed by 8 bones which articulate with radius and ulna on one side and provide articulation to carpometacarpal joints on the other side.
Hand originates at the wrist as five metacarpal bones. These can be felt in the region of hand that is occupied by palm. Phalanges are small bones that form the skeleton of fingers and thumb. There are a total of 14 phalanges, two for the thumb, and three for each finger. The phalanx that articulates with metacarpal bone is called the proximal phalanx. The terminal phalanx is called the distal phalanx. Thumb contains only these two phalanges. A third phalanx called middle phalanx. Phalanges articulate with each other at interphalangeal joints.
What are Functions of Upper Limb
The hand is the most evolved organ in the upper limb and most of our abilities to do work are reflected by our hand functions.
Rest of the upper limb from shoulder to forearm functions to position the hand at the desirable place.
They are designed to put your hand where you want it to be, doing what you want it to do.
They put the hand into desirable position. They lift and rotate to reach something. Apart from enabling hand reach something, they also stabilize the limb so that hand could function to its best.
The hand is a marvelous organ. It performs precise and gross jobs with equal ease, facilitated by small bones, multiple joints and many small muscles both intrinsic and extrinsic.
Hands could be gentle and tough. They can perform precise functions like writing, painting, playing musical instruments. They also enable us to perform heavy labor like using a shovel, an axe or a drill etc.
Apart from these motor functions, we also use our hands for sensory functions. We use them to feel if something is warm or cold, smooth or rough.
Upper limb motions are also parts of gestures. Since early times we are using the upper limb to make signs to approve, nod, call for help or stop. Remember goodbyes!
Thus our hands are important in communication, and we also use them while we talk to emphasize, compliment or dramatize our verbal communications.
Upper limbs have a phenomenal reach around us in all the planes. This is made possible by the presence of highly mobile shoulder girdle.
That is why we can reach behind our head for grooming, or to stretch forward to grasp, take off your shoe with an ease that we hardly think about.