The Upper Limb: Nerves, Arteries, and Veins – Structure and Function

This article will provide an overview of the nervous, arterial, and venous systems of the upper limb, covering their structures, functions, and important considerations.

I. Nervous System of the Upper Limb

1. Radial Nerve

• Arm Region:

• Originates from the posterior cord of the brachial plexus, travels through the triangular space (along with the deep brachial artery) to enter the posterior arm.

• Lies closely to the radial groove of the humerus.

• Pierces the lateral intermuscular septum and moves to the anterior arm, within the lateral bicipital groove of the cubital fossa.

• Splits into two branches descending into the forearm.

• Function:

• Provides motor innervation to the triceps brachii muscle.

• Provides sensory innervation to the skin of the lateral and posterior arm.

• Elbow and Forearm Regions:

• Divides into two branches:

• Superficial branch: Passes through the joint capsule, descends posterior to the brachioradialis muscle, anterior to the extensor carpi radialis longus muscle, emerges dorsally, and becomes subcutaneous approximately 3 cm above the radial styloid process to provide sensation to the lateral half of the dorsum of the hand.

• Deep branch (posterior interosseous nerve): Travels between the two layers of extensor muscles, giving off numerous branches between the two muscle layers of the posterior forearm to innervate the muscles in this region. Note: The deep branch innervates all the muscles of the posterior forearm, except the brachioradialis and extensor carpi radialis longus muscles, which are innervated by the lateral branches of the radial nerve.

• Hand Region: The radial nerve does not descend into the hand, it only provides sensory innervation to the lateral three and a half digits of the dorsal hand.

2. Ulnar Nerve

• Arm Region:

• Originates from the medial cord of the brachial plexus.

• Descends along the brachial artery in the arm.

• Pierces the medial intermuscular septum and emerges into the posterior arm at the middle third of the arm.

• Passes through the ulnar groove at the elbow and descends into the forearm.

• In the arm, the ulnar nerve does not give off any lateral branches.

• Forearm Region:

• Travels anterior to the flexor digitorum profundus muscle and posterior to the flexor carpi ulnaris muscle.

• The ulnar artery accompanies the ulnar nerve in the lower two-thirds of the forearm, located lateral to the ulnar nerve.

• Above the wrist, the ulnar nerve gives off a motor branch to one and a half muscles: the flexor carpi ulnaris muscle and the medial half of the flexor digitorum profundus muscle (fourth and fifth digits).

• It travels lateral to the pisiform bone and anterior to the flexor retinaculum to enter the hand.

• Hand Region:

• Enters the hand between the pisiform bone and the hamate bone, anterior to the flexor retinaculum, posterior to the palmaris brevis muscle, and then divides into two branches:

• Superficial branch: Provides sensory innervation to the medial one and a half digits (fifth digit and half of the fourth digit) and provides a motor branch to the palmaris brevis muscle.

• Deep branch: Innervates the remaining three muscles of the hypothenar eminence, loops around the hamate bone, penetrates deep into the hand, innervates all remaining palmar muscles except the five muscles innervated by the median nerve: the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and the first and second lumbricals.

3. Median Nerve

• Arm Region:

• Originates from the medial and lateral roots of the brachial plexus, travels alongside the brachial artery within the brachial canal.

• Superiorly, the median nerve lies anterolaterally to the artery; it then crosses anterior to the artery to descend, located within the artery.

• In the arm, the median nerve does not give off any branches.

• Forearm Region:

• Travels from the middle of the cubital fossa to the middle of the wrist crease.

• It lies deep to the pronator teres muscle, deeper than the superficial layer of forearm muscles (including the flexor digitorum superficialis, palmaris longus, and flexor carpi radialis muscles).

• It crosses the ulnar artery in the upper third of the forearm.

• It innervates all the muscles of the anterior forearm except for one and a half muscles innervated by the ulnar nerve.

• The motor branch to the pronator quadratus muscle is specifically referred to as the anterior interosseous nerve.

• In the lower third of the forearm, the median nerve travels alongside the four tendons of the flexor digitorum superficialis muscle, situated most laterally and superficially compared to these tendons.

• Hand Region:

• Enters the hand posterior to the flexor retinaculum.

• Upon exiting the carpal tunnel, the nerve lies posterior to the palmar fascia.

• It provides sensory innervation to the lateral three and a half digits of the hand and motor innervation to five muscles: the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and the first and second lumbricals.

4. Musculocutaneous Nerve

• Origin: From the lateral cord of the brachial plexus.

• Course: Passes through the coracobrachialis muscle, travels between the biceps brachii and brachialis muscles, reaches the lateral bicipital groove, pierces the superficial fascia, and divides into two sensory branches for the lateral forearm.

• Function:

• Provides motor innervation to the muscles of the anterior arm (coracobrachialis, biceps brachii, and brachialis muscles).

• Provides sensory innervation to the lateral forearm.

5. Axillary Nerve

• Origin: From the posterior cord of the brachial plexus.

• Course: Travels with the posterior circumflex humeral artery, passes through the quadrangular space to loop around the surgical neck of the humerus.

• Function: Innervates the deltoid muscle.

6. Medial Brachial Cutaneous Nerve

• Origin: From the medial cord of the brachial plexus.

• Course: Travels through the superficial fascia.

• Function: Provides sensory innervation to the lower medial aspect of the arm.

7. Medial Antebrachial Cutaneous Nerve

• Origin: From the medial cord of the brachial plexus.

• Course: Travels within the brachial canal until the middle third of the arm, then pierces the superficial fascia.

• Function: Provides sensory innervation to the lower medial aspect of the arm and the medial forearm.

II. Arterial System of the Upper Limb

1. Axillary Artery

• Course: It is the continuation of the subclavian artery, extending from the midpoint of the posterior border of the clavicle to the inferior border of the teres major muscle, where it changes its name to the brachial artery.

• Lateral Branches: Has six branches:

• Superior thoracic artery: Supplies blood to the pectoral muscles.

• Thoracoacromial artery: Supplies blood to the shoulder and chest.

• Lateral thoracic artery: Supplies blood to the chest wall.

• Subscapular artery: Supplies blood to the posterior axillary fossa.

• Anterior circumflex humeral artery and posterior circumflex humeral artery: Enter the deltoid muscle, anastomosing around the surgical neck of the humerus.

Note: The axillary artery commonly anastomoses with the subclavian artery and the brachial artery, forming three anastomotic circles around the shoulder, chest, and arm regions:

• Thoracic circle: Formed by the lateral thoracic artery and the thoracoacromial artery anastomosing with the internal thoracic artery and the superior intercostal artery of the subclavian artery.

• Shoulder circle: Formed by the subscapular artery anastomosing with the suprascapular artery and the posterior scapular artery of the subclavian artery.

• Humeral circle: Formed by the anterior circumflex humeral artery anastomosing with the posterior circumflex humeral artery and the deep brachial artery of the brachial artery.

Note: Because the shoulder and chest circles do not connect to the humeral circle, ligation of the axillary artery between the anterior circumflex humeral artery and the subscapular artery can be dangerous.

2. Brachial Artery

• Course: It follows the axillary artery, extending from the inferior border of the teres major muscle to 3 cm below the cubital fossa, where it divides into two branches: the radial artery and the ulnar artery.

• Lateral Branches: Includes the following main branches:

• Deep brachial artery: Emerges into the posterior arm.

• Superior ulnar collateral artery: Travels with the ulnar nerve downwards.

• Inferior ulnar collateral artery.

• Ulnar artery

• Radial artery

3. Ulnar Artery

• Course: It is the terminal branch of the brachial artery, starting 3 cm below the cubital fossa, traveling down to the wrist and into the palm, forming the superficial palmar arch.

• Lateral Branches: Has lateral branches that supply the forearm and hand. One of these branches, the deep palmar branch, anastomoses with the radial artery to form the deep palmar arch.

4. Radial Artery

• Course: It starts 3 cm below the cubital fossa, descends within the radial groove, then loops around the radial styloid process, travels through the anatomical snuffbox, and enters the palm to form the deep palmar arch.

• Lateral Branches: Has lateral branches that supply the forearm and hand. One of these branches, the superficial palmar branch, anastomoses with the ulnar artery to form the superficial palmar arch.

5. Superficial Palmar Arch

• Formation: Formed by the ulnar artery anastomosing with the superficial palmar branch of the radial artery.

• Lateral Branches: Provides branches that supply the hand and fingers.

6. Deep Palmar Arch

• Formation: Formed by the radial artery anastomosing with the deep palmar branch of the ulnar artery.

• Lateral Branches: Provides branches that supply the hand and fingers.

III. Venous System of the Upper Limb

1. Deep Veins

• Course: From the lower region up to the arm, there are usually two deep veins accompanying each artery of the same name. They merge in the axillary fossa to form the axillary vein.

2. Superficial Veins

• Course: Within the subcutaneous fat of the dorsum of the hand, there is a rich venous network. This network drains into three superficial veins: the cephalic vein, the intermediate vein, and the basilic vein, from medial to lateral. These veins ascend to the antecubital fossa to contribute to the venous network. The basilic vein and the cephalic vein continue upwards to drain into the axillary vein.

IV. Considerations

• Understanding the structure and function of the nervous, arterial, and venous systems of the upper limb is crucial for the diagnosis and treatment of pathologies related to the upper limb.

• Injuries to the nerves, arteries, or veins of the upper limb can lead to severe complications, such as paralysis, pain, tissue damage, and even necrosis.

• Therefore, it is essential to protect the upper limb from injuries and adverse effects.

• If you experience any unusual symptoms in your upper limb, consult a physician for prompt examination and advice.

This article aims to provide you with helpful information about the structure and function of the nerves, arteries, and veins of the upper limb.