The upper limb is attached to the trunk by muscles and a small skeletal articulation at the sternoclavicular joint.

The upper limb is divided into the shoulder, arm, forearm, and hand based on the position of its major joints and component bones.

The shoulder is defined as the area of upper limb attachment to the trunk.

The arm is the part of the upper limb located between the shoulder and the elbow joint.

The forearm is the part of the upper limb situated between the elbow joint and the wrist joint.

The hand is the part of the upper limb distal to the wrist joint.

The axilla is an irregularly shaped pyramidal area formed by the muscles and bones of the shoulder and the lateral surface of the thoracic wall. Its apex opens into the lower neck, and the skin of the armpit forms its floor. All major structures passing between the neck and arm traverse the axilla.

The cubital fossa is a triangular depression anterior to the elbow joint, formed by muscles. It is a passage for the brachial artery and the median nerve.

The carpal tunnel is the gateway to the palm, formed by carpal bones and the flexor retinaculum. It transmits the median nerve and long flexor tendons to the digits.

Unlike the lower limb, the upper limb is highly mobile, primarily used for positioning the hand in space.

Sliding (protraction and retraction) and rotating the scapula on the thoracic wall alters the position of the glenohumeral joint, extending the reach of the hand.

The glenohumeral joint allows for a wide range of motion in three axes: flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction.

The major movements at the elbow joint are flexion and extension of the forearm.

Pronation is the movement where the radius crosses over the ulna, turning the palm posteriorly. Supination returns the hand to the anatomical position (palm anterior).

The wrist joint allows for abduction, adduction, flexion, extension, and circumduction of the hand.

The hand functions as a mechanical tool for gripping and manipulating objects, involving finger flexion against the thumb and coordinated joint movements.

The hand is a crucial sensory tool for discriminating objects by touch, due to a high density of sensory receptors in the finger pads and a disproportionately large representation in the sensory cortex.

The bones of the shoulder include the scapula, clavicle, and the proximal end of the humerus.

The humerus is the single bone of the arm.

The forearm consists of two bones: the radius (lateral) and the ulna (medial).

The elbow joint is a hinge joint formed by the distal humerus articulating with the proximal radius and ulna, allowing flexion and extension. It also permits the radius to spin on the ulna for pronation/supination.

The wrist joint is formed between the radius and carpal bones, and an articular disc distal to the ulna and carpal bones.

The bones of the hand include the carpal bones (wrist), metacarpals (palm), and phalanges (digits).

The thumb has two phalanges, while the other four digits each have three phalanges.

These are biaxial condylar joints allowing abduction, adduction, flexion, extension, and circumduction of the fingers.

These are primarily hinge joints that permit only flexion and extension of the fingers.

Muscles like the trapezius, levator scapulae, and rhomboids connect the scapula and clavicle to the trunk.

Muscles such as the pectoralis major, latissimus dorsi, teres major, and deltoid connect the clavicle, scapula, and body wall to the proximal humerus.

The four rotator cuff muscles (subscapularis, supraspinatus, infraspinatus, teres minor) connect the scapula to the humerus and stabilize the glenohumeral joint.

Muscles in the arm are divided into anterior (flexor) and posterior (extensor) compartments by fascia and intermuscular septa.

The forearm's anterior and posterior compartments are separated by a lateral intermuscular septum, the radius, ulna, and an interosseous membrane.

Intrinsic muscles of the hand produce delicate digit movements and modify forces from forearm tendons. The thenar muscles form the thenar eminence and allow thumb mobility.

The axillary inlet at the base of the neck is bordered by the lateral margin of rib I, the posterior surface of the clavicle, the superior margin of the scapula, and the medial surface of the coracoid process.

The upper limb is innervated by the brachial plexus, formed from spinal nerves C5-T1, which originates in the neck and passes through the axillary inlet into the axilla.

Muscles like the trapezius, levator scapulae, rhomboid major, rhomboid minor, and latissimus dorsi connect the shoulder girdle bones to the back and thoracic wall.

The breast overlies the pectoralis major muscle (anterior axillary wall), and its axillary process can extend into the axilla. Lymphatic drainage from the breast often goes to axillary lymph nodes.

The brachial plexus, formed by the anterior rami of spinal nerves C5 to T1, is the primary source of innervation for the upper limb.

Testing dermatomes, myotomes, and tendon reflexes in the upper limb is used to clinically assess lower cervical and T1 nerve function.

The upper lateral region of the arm is a key area for testing sensation related to the C5 spinal cord level.

The palmar pad of the thumb is a key area for testing sensation related to the C6 spinal cord level.

The pad of the index finger is a key area for testing sensation related to the C7 spinal cord level.

The pad of the little finger is a key area for testing sensation related to the C8 spinal cord level.

The skin on the medial aspect of the elbow is a key area for testing sensation related to the T1 spinal cord level.

Abduction of the arm at the glenohumeral joint is predominantly controlled by the C5 nerve root.

Flexion of the forearm at the elbow joint is primarily controlled by the C6 nerve root.

Extension of the forearm at the elbow joint is mainly controlled by the C7 nerve root.

Flexion of the fingers is mainly controlled by the C8 nerve root.

Abduction and adduction of the index, middle, and ring fingers are predominantly controlled by the T1 nerve root.

Tapping the biceps tendon in the cubital fossa primarily tests the C6 spinal cord level.

Tapping the triceps tendon posterior to the elbow primarily tests the C7 spinal cord level.

All muscles in the anterior compartment of the arm are innervated by the musculocutaneous nerve.

The median nerve innervates most muscles in the anterior forearm, with exceptions for flexor carpi ulnaris and part of flexor digitorum profundus (ulnar nerve).

Most intrinsic hand muscles are innervated by the ulnar nerve, except for thenar muscles and lateral lumbricals (median nerve).

All muscles in the posterior compartments of the arm and forearm are innervated by the radial nerve.

The musculocutaneous nerve provides sensation to the skin on the anterolateral side of the forearm.

The median nerve provides sensation to the palmar surface of the lateral three and a half digits.

The ulnar nerve provides sensation to the medial one and a half digits.

The radial nerve supplies skin on the posterior surface of the forearm and the dorsolateral surface of the hand.

The axillary nerve passes around the posterior aspect of the surgical neck of the humerus, making it vulnerable to injury in fractures of this region.

The radial nerve travels diagonally around the posterior surface of the middle of the humerus in the radial groove, making it susceptible to injury with midshaft humeral fractures.

The ulnar nerve passes posteriorly to the medial epicondyle of the distal humerus, explaining the 'funny bone' sensation when this area is struck.

Large superficial veins like the cephalic, basilic, and median cubital veins are commonly used for vascular access and blood withdrawal.

The cephalic vein originates from the dorsal venous network of the hand, ascends laterally, crosses the elbow, and passes through the deltopectoral triangle into the axilla.

The basilic vein originates from the medial dorsal venous network of the hand, ascends posteromedially on the forearm, moves anteriorly below the elbow, and penetrates deep fascia in the mid-arm.

The median cubital vein connects the cephalic and basilic veins at the elbow, crossing the roof of the cubital fossa and serving as a common site for venipuncture.

The thumb is oriented at a right angle to the other digits, allowing its movements to occur in a plane perpendicular to the other fingers.

The ability to bring the pad of the thumb into contact with the pads of the other fingers (opposition) is crucial for normal hand function and is facilitated by the thumb's unique articulation and musculature.