Bracgial plexuses
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brachial plexus anatomy roots trunks divisions cords branches
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I now have comprehensive information from Gray's Anatomy for Students. Here is the full detailed answer:
Brachial Plexus
The brachial plexus is a somatic nerve plexus formed by the anterior rami of C5 to C8, and most of T1. It originates in the neck, passes laterally and inferiorly over rib I, and enters the axilla. It is the sole nerve supply for the entire upper limb.
Overview Diagram
Major components in the neck and axilla showing roots, trunks, divisions and cords (Gray's Anatomy for Students)
Schematic of the brachial plexus from roots to terminal nerves (Gray's Anatomy for Students)
Mnemonic
Real Tea Drinks Cold Beer = Roots → Trunks → Divisions → Cords → Branches
Parts of the Brachial Plexus
1. Roots (Anterior Rami)
The roots of the brachial plexus are the anterior rami of C5 to C8, and most of T1. They pass between the anterior and middle scalene muscles and lie superior and posterior to the subclavian artery. Gray rami communicantes from the sympathetic trunk join the roots here, carrying postganglionic sympathetic fibers to the periphery.
2. Trunks
Three trunks form from the roots:
| Trunk | Formation |
|---|---|
| Superior (upper) | Union of C5 + C6 |
| Middle | Continuation of C7 alone |
| Inferior (lower) | Union of C8 + T1 |
The inferior trunk lies on rib I posterior to the subclavian artery; the middle and superior trunks are more superior.
3. Divisions
Each trunk splits into an anterior and a posterior division:
- The 3 anterior divisions give rise to parts supplying the anterior (flexor) compartments
- The 3 posterior divisions combine to supply the posterior (extensor) compartments
- No peripheral nerves originate directly from divisions
4. Cords
Named by their position relative to the 2nd part of the axillary artery:
| Cord | Formation | Roots |
|---|---|---|
| Lateral cord | Anterior divisions of superior + middle trunks | C5-C7 |
| Medial cord | Anterior division of inferior trunk | C8, T1 |
| Posterior cord | All three posterior divisions | C5-T1 |
Complete Branches Diagram
All branches of the brachial plexus and their relationship to the axillary artery (Gray's Anatomy for Students)
Branches
From the Roots
| Nerve | Root | Motor Supply |
|---|---|---|
| Dorsal scapular nerve | C5 | Rhomboid major, rhomboid minor |
| Long thoracic nerve | C5, C6, C7 | Serratus anterior |
| Contribution to phrenic nerve | C5 | Diaphragm (partial) |
From the Superior Trunk
| Nerve | Spinal Segments | Supply |
|---|---|---|
| Suprascapular nerve | C5, C6 | Supraspinatus, infraspinatus |
| Nerve to subclavius | C5, C6 | Subclavius muscle |
From the Lateral Cord
| Nerve | Spinal Segments | Supply |
|---|---|---|
| Lateral pectoral nerve | C5-C7 | Pectoralis major (clavicular head) |
| Musculocutaneous nerve | C5-C7 | Coracobrachialis, biceps brachii, brachialis; then becomes lateral cutaneous nerve of forearm |
| Lateral root of median nerve | C5-C7 | (Joins medial root to form median nerve) |
From the Medial Cord
| Nerve | Spinal Segments | Supply |
|---|---|---|
| Medial pectoral nerve | C8, T1 | Pectoralis major and minor |
| Medial cutaneous nerve of arm | C8, T1 | Skin over medial distal 1/3 of arm |
| Medial cutaneous nerve of forearm | C8, T1 | Skin over medial forearm down to wrist |
| Ulnar nerve | C8, T1 | Flexor carpi ulnaris, medial 1/2 of flexor digitorum profundus, most intrinsic hand muscles |
| Medial root of median nerve | C8, T1 | (Joins lateral root to form median nerve) |
From the Posterior Cord
| Nerve | Spinal Segments | Supply |
|---|---|---|
| Superior subscapular nerve | C5, C6 | Subscapularis (upper) |
| Thoracodorsal nerve | C6-C8 | Latissimus dorsi |
| Inferior subscapular nerve | C5, C6 | Subscapularis (lower), teres major |
| Axillary nerve | C5, C6 | Deltoid, teres minor; skin over deltoid (upper lateral cutaneous nerve of arm) |
| Radial nerve | C5-C8, T1 | All muscles of posterior arm and forearm; skin over posterior limb |
Median Nerve
Formed anterior to the 3rd part of the axillary artery by the union of the lateral root (from lateral cord, C5-C7) and medial root (from medial cord, C8-T1). It supplies:
- Most anterior forearm muscles (except flexor carpi ulnaris and medial 1/2 FDP)
- Three thenar muscles + two lateral lumbricals in the hand
- Skin over palmar surface of lateral 3.5 digits
The "M" Pattern in the Axilla
The musculocutaneous nerve, lateral cord, median nerve, medial cord, and ulnar nerve form a characteristic "M" or "W" shape over the 3rd part of the axillary artery. This is a key landmark for identifying brachial plexus components during surgery or dissection.
Clinical Summary of Key Injuries
| Injury | Roots | Mechanism | Classic Deficit |
|---|---|---|---|
| Erb's palsy | C5, C6 | Shoulder dystocia / fall on shoulder | "Waiter's tip" - arm adducted, internally rotated, elbow extended, forearm pronated |
| Klumpke's palsy | C8, T1 | Traction on abducted arm | Claw hand; if T1 preganglionic - Horner syndrome |
| Saturday night palsy | Radial nerve | Compression in spiral groove | Wrist drop |
| Serratus anterior palsy | Long thoracic (C5-7) | Carrying heavy loads | Medial winging of scapula |
| Axillary nerve injury | C5, C6 | Anterior shoulder dislocation | Deltoid weakness, loss of sensation over deltoid regio |
- Gray's Anatomy for Students, pp. 858-865
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