Last Updated on March 8, 2025
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 the 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 superior reach and grasp.
The upper and lower limbs develop from buds that begin to form in 4th week of fetal life. all the connective tissue structures like muscle, bone, blood vessels, and lymphatics are all formed from the mesoderm. The peripheral nerves are differentiated neural crest cells.
Parts of the Upper Limb
The upper limb can be divided into the following parts
- Shoulder Region
- Arm (or brachium)
- Forearm (or antebrachium)
- Hand (or manus).
Shoulder Region
The 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 comprises parts around the scapula. The bones of the shoulder girdle are the clavicle and the scapula.
Arm
Also called the 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
The 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.
Hand (Manus)
Hand includes
- 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
There are a total of thirty bones in the upper limb. These provide shape and act as a framework for the muscles, blood vessels, nerves, and lymphatics.
Clavicle
The clavicle is the bone that connects the shoulder girdle to the thorax. On one side it articulates with the sternum at the sternoclavicular joint and on the other side, it articulates with the acromion process of the scapula at the acromioclavicular joint
Scapula
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 the humerus called the shoulder joint or scapulohumeral joint). It also has a gliding motion with thorax at its inner surface. This gliding action adds to the mobility of the shoulder joint.
Humerus
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
The forearm contains two bones-radius and ulna. The ulna forms the elbow joint with the lower end of the humerus. Radius and ulna articulate with each other at superior and inferior radio-ulnar joints. These joints allow movements of pronation and supination.
Wrist
The wrist or carpus is formed by 8 bones that articulate with radius and ulna on one side and provide articulation to carpometacarpal joints on the other side.
Hand
The hand originates at the wrist as five metacarpal bones. These can be felt in the region of the hand that is occupied by the 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 the metacarpal bone is called the proximal phalanx. The terminal phalanx is called the distal phalanx. The thumb contains only these two phalanges. A third phalanx is called the middle phalanx is present between the proximal and distal phalanx in all digits except the thumb. Phalanges articulate with each other at interphalangeal joints.
Blood Supply
The arterial supply of the upper limb starts with the subclavian artery. The subclavian artery, in the axilla, becomes an axillary artery and passes deep to the pectoralis minor muscle toward the humerus. It gives off the anterior and posterior circumflex humeral arteries around the humerus head and becomes the brachial artery after passing teres minor to give off the profunda brachii, which supplies the deep structures of the arm. INear elbow, it divides into radial artery and ulnar artery which supply forearm and hand.
The venous drainage of the upper extremity is accomplished via the basilic vein that courses along the medial side of the arm and the cephalic vein arises around the hand and transverses the anterolateral area of the upper limb.
Nerves
The brachial plexus supplies all the nerves in the upper extremity.
The five major branches of the plexus are the musculocutaneous, axillary, median, radial, and ulnar nerve.
- Musculocutaneous nerve (C5, C6, C7): It provides motor supply to the three muscles of the anterior arm, the biceps brachii, brachialis, and coracobrachialis, as well as sensory innervation to the radial side of the forearm.
- Axillary Nerve (C5, C6): It supplies the deltoid muscle and the teres minor. It also provides sensory innervation via the upper lateral cutaneous nerve of the arm.
- Median nerve (C6-T1): It supplies the flexor muscles of the anterior forearm except flexor digitorum profundus, the deep compartment of the anterior forearm via anterior interosseous. Its branch, the palmar cutaneous nerve, innervates the skin over the radial surface of the palm. Further down it supplies sensory innervation to the radial 3.5 digits and the palmar surface as well as motor innervation to the two radial lumbricals.
- Radial nerve(C5-T1): It supplies motor the most of the muscles in the posterior compartment of the forearm, while the superficial branch supplies sensory innervation to the posterior surface of the hand and fingers.
- Ulnar nerve (C8-T1): It supplies the ulnar half of the flexor digitorum profundus muscle and the flexor carpi ulnaris. The cutaneous branches also supply the sensation to the little finger and ulnar half of the ring finger.
Muscles
The musculature of the upper limb is quite vast, much more so than the lower extremity.
Upper Arm
- Anterior Compartment: Contains three muscles in the anterior compartment- Biceps brachii, coracobrachialis, brachialis are deep to the biceps.
- Posterior compartment: Contains only one muscle, the triceps brachii
Anterior Forearm
- Superficial Compartment: flexor carpi radialis, flexor carpi ulnaris, palmaris longus, and pronator teres
- Intermediate Compartment: Flexor digitorum superficialis
- Deep: Flexor digitorum profundus, flexor pollicus longus, and pronator quadratus.
Posterior Forearm
- Superficial Compartment: Anconeus, brachioradialis, extensor carpi radialis longus and brevis, extensor carpi ulnaris, extensor digitorum, and extensor digiti minimi.
- Deep compartment: Abductor pollicis longus, extensor indicis, extensor pollicis longus and brevis, and supinator.
Hand
- Thenar muscles: Located at the thumb- Abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
- Hypothenar muscles: Located on side of little finger- Aabductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi.
- Third Group: Palmaris brevis, adductor pollicis, Dorsal interossei, palmar interossei, Lumbrical muscles
Functions of the 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. The 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 a desirable position. They lift and rotate to reach something. Apart from enabling the hand to reach something, they also stabilize the limb so that the hand can function at 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 communication.
Upper limbs have a phenomenal reach around us in all the planes. This is made possible by the presence of a 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.
