Brachial Plexus and Upper Limb Anatomy

Brachial Plexus Anatomy

The brachial plexus is a network of nerves that originates from the spinal cord and supplies the upper limb. It is divided into roots, trunks, divisions, cords, and branches.

Roots

The brachial plexus is formed by the anterior rami of the spinal nerves C5, C6, C7, C8, and T1.

Trunks

• Upper trunk: Formed by the union of the C5 and C6 roots.
• Middle trunk: Continuation of the C7 root.
• Lower trunk: Formed by the union of the C8 and T1 roots.

Divisions

Each trunk splits into an anterior and a posterior division:

• Anterior divisions: Generally supply the flexor muscles of the arm.
• Posterior divisions: Generally supply the extensor muscles.

Cords

The divisions regroup to form three cords named based on their position relative to the axillary artery:

• Lateral cord: Formed from the anterior divisions of the upper and middle trunks.
• Posterior cord: Formed from all three posterior divisions.
• Medial cord: Formed from the anterior division of the lower trunk.

Branches

The cords give rise to the major nerves of the upper limb:

• Musculocutaneous nerve: Arises from the lateral cord.
• Axillary nerve: Arises from the posterior cord.
• Radial nerve: Arises from the posterior cord.
• Median nerve: Formed by contributions from the lateral and medial cords.
• Ulnar nerve: Arises from the medial cord.

Upper Limb Anatomy

The upper limb consists of the shoulder, arm (brachium), forearm (antebrachium), and hand. Here are the key anatomical features:

Shoulder

• Bones: Clavicle, scapula, and humerus.
• Joints: Glenohumeral joint (shoulder joint), acromioclavicular joint, and sternoclavicular joint.
• Muscles: Deltoid, rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis), and others.

Arm (Brachium)

• Bones: Humerus.
• Muscles: Biceps brachii, triceps brachii, brachialis, and coracobrachialis.

Forearm (Antebrachium)

• Bones: Radius and ulna.
• Muscles: Divided into flexors (e.g., flexor carpi radialis, flexor carpi ulnaris, palmaris longus) and extensors (e.g., extensor carpi radialis longus, extensor carpi ulnaris).

Hand

• Bones: Carpals (wrist bones), metacarpals (palm bones), and phalanges (finger bones).
• Muscles: Intrinsic muscles (e.g., thenar and hypothenar muscles, lumbricals, interossei) and extrinsic muscles (originating in the forearm).

Nerve Innervation

Each major nerve of the brachial plexus innervates specific muscles and skin areas in the upper limb:

• Musculocutaneous nerve: Innervates the biceps brachii, brachialis, and coracobrachialis muscles; provides sensation to the lateral forearm.
• Axillary nerve: Innervates the deltoid and teres minor muscles; provides sensation to the skin over the deltoid.
• Radial nerve: Innervates the triceps brachii and extensor muscles of the forearm; provides sensation to the posterior arm and forearm, and the dorsal hand.
• Median nerve: Innervates most of the flexor muscles in the forearm, thenar muscles, and lateral two lumbricals; provides sensation to the palmar side of the thumb, index, middle, and half of the ring finger.
• Ulnar nerve: Innervates the flexor carpi ulnaris, part of the flexor digitorum profundus, and most intrinsic hand muscles; provides sensation to the palmar and dorsal aspect of the little finger and medial half of the ring finger.