Brachial plex
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The brachial plexus is a network of nerves (C5-T1) that innervates the upper limb. It forms from the ventral rami of the lower cervical and upper thoracic spinal nerves, organizing into roots, trunks, divisions, cords, and terminal branches.
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Here is a complete overview of the Brachial Plexus, sourced from Gray's Anatomy for Students.
Brachial Plexus
The brachial plexus is a somatic nerve plexus formed by the anterior rami of C5-C8 and most of T1. It originates in the neck, passes laterally and inferiorly over rib I, and enters the axilla. It is organized into five sequential levels: Roots → Trunks → Divisions → Cords → Branches.
(Gray's Anatomy for Students, Fig. 7.53 - Schematic [A] and anatomical relationships [B])
1. Roots (C5-T1)
The roots are the anterior rami of spinal nerves C5-C8 and T1. They pass between the anterior and middle scalene muscles and receive gray rami communicantes from the sympathetic trunk (postganglionic sympathetic fibers).
Branches from the roots:
- Dorsal scapular nerve (C5) - innervates rhomboid major and minor
- Long thoracic nerve (C5-C7) - innervates serratus anterior
- Small contribution of C5 to the phrenic nerve
2. Trunks
| Trunk | Origin |
|---|---|
| Superior (upper) | C5 + C6 |
| Middle | C7 alone |
| Inferior (lower) | C8 + T1 |
The inferior trunk lies on rib I posterior to the subclavian artery. The trunks cross the base of the posterior triangle of the neck.
Branches from the trunks (superior trunk only):
- Suprascapular nerve (C5-C6) - innervates supraspinatus and infraspinatus
- Nerve to subclavius (C5-C6) - innervates subclavius muscle
3. Divisions
Each trunk splits into an anterior and a posterior division (6 divisions total). No peripheral nerves originate directly from the divisions.
- Anterior divisions - give rise to nerves of the anterior (flexor) compartments
- Posterior divisions - all three combine to supply posterior (extensor) compartments
4. Cords
The cords are named by their relationship to the second part of the axillary artery:
| Cord | Formation | Roots | Position |
|---|---|---|---|
| Lateral | Anterior divisions of superior + middle trunks | C5-C7 | Lateral to axillary artery |
| Medial | Anterior division of inferior trunk | C8-T1 | Medial to axillary artery |
| Posterior | All three posterior divisions | C5-T1 | Posterior to axillary artery |
Branches from the cords:
Lateral cord:
- Lateral pectoral nerve - pectoralis major
- Musculocutaneous nerve - coracobrachialis, biceps, brachialis; terminates as lateral cutaneous nerve of forearm
- Lateral root of median nerve
Medial cord:
- Medial pectoral nerve - pectoralis minor (and major)
- Medial cutaneous nerve of arm
- Medial cutaneous nerve of forearm
- Ulnar nerve
- Medial root of median nerve
Posterior cord:
- Superior subscapular nerve - subscapularis
- Thoracodorsal nerve - latissimus dorsi
- Inferior subscapular nerve - subscapularis and teres major
- Axillary nerve (C5-C6) - deltoid and teres minor
- Radial nerve (C5-T1) - posterior compartments of arm and forearm
5. Terminal Branches (the "5 big nerves")
| Nerve | Cord Origin | Key Motor Function |
|---|---|---|
| Musculocutaneous | Lateral | Flexors of arm (biceps, brachialis, coracobrachialis) |
| Median | Lateral + Medial roots | Flexors of forearm, thenar muscles |
| Ulnar | Medial | Intrinsic hand muscles, hypothenar |
| Radial | Posterior | Extensors of arm and forearm |
| Axillary | Posterior | Deltoid, teres minor |
Key Clinical Injuries
| Injury | Roots | Classic Presentation |
|---|---|---|
| Erb's palsy (upper trunk) | C5-C6 | "Waiter's tip" - arm adducted, medially rotated, elbow extended, forearm pronated |
| Klumpke's palsy (lower trunk) | C8-T1 | Intrinsic hand muscle weakness, claw hand; ± Horner syndrome if T1 sympathetics involved |
| Winging of scapula | C5-C7 (long thoracic nerve) | Serratus anterior paralysis |
| Saturday night palsy | Posterior cord/radial nerve | Wrist drop |
Mnemonic for the levels: Real Texans Drink Cold Beer (Roots - Trunks - Divisions - Cords - Branches)
- Gray's Anatomy for Students, pp. 858-862
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