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Brachial Plexus Anatomy

Kristin Barkley, DNP, CRNA

Quick Facts
Anatomy
Peripheral Nerve Branches & Innervations
Regional Blocks
Injury Considerations
Media
References

Brachial Plexus

  • The brachial plexus provides motor and sensory innervation to nearly all of the shoulder and upper extremity.
  • Originates from the ventral rami of five spinal nerve roots: C5–T1.
  • Roots pass between the anterior scalene muscle (ASM) and middle scalene muscle (MSM) after exiting their vertebral foramina.
  • Organization: Roots → Trunks → Divisions → Cords → Branches (“Read That Darn Cadaver Book” mnemonic).
  • These five roots merge and divide to form:
    • 3 Trunks: Upper, Middle, Lower
    • 6 Divisions: 3 Anterior, 3 Posterior
    • 3 Cords: Posterior, Medial, Lateral

 

Anatomy

Trunks

As the nerves emerge between the scalene muscles, they travel laterally across the posterior triangle of the neck:

  • Upper Trunk: C5–C6
  • Middle Trunk: C7
  • Lower Trunk: C8–T1

Divisions

At the lateral border of the first rib and posterior to the clavicle, each trunk divides into:

  • Three anterior divisions
  • Three posterior divisions

Cords

Divisions enter the axilla and are named according to their relationship to the axillary artery:

  • Posterior Cord: posterior divisions of all three trunks.
  • Medial Cord: anterior division of the inferior trunk.
  • Lateral Cord: anterior divisions of the superior and middle trunks.

 

Peripheral Nerve Branches & Innervations

Terminal Branches

  • Posterior Cord: axillary and radial nerves
  • Lateral + Medial Cords: median nerve
  • Lateral Cord: musculocutaneous nerve
  • Medial Cord: ulnar nerve

Major Nerve Innervations

Median Nerve (C6–T1)

  • Motor: flexors of the forearm and hand (index and middle fingers)
  • Sensory: palmar cutaneous branch — lateral 3½ digits on palmar surface

Ulnar Nerve (C8–T1)

  • Motor: flexor carpi ulnaris, intrinsic hand muscles
  • Sensory: anterior and posterior medial 1½ digits and palm

Musculocutaneous Nerve (C5–C7)

  • Motor: biceps brachii, brachialis, coracobrachialis
  • Sensory: lateral forearm (via lateral cutaneous branch)

Axillary Nerve (C5–C6)

  • Motor: deltoid and teres minor
  • Sensory: superior lateral cutaneous nerve — inferior deltoid region

Radial Nerve (C5–T1)

  • Motor: extensor muscles of upper arm, forearm, and hand
  • Sensory: posterior arm/forearm and posterolateral hand

 

Regional Blocks

  • Interscalene Block
  • Suprascapular Block
  • Axillary Block
  • Supraclavicular Block
  • Infraclavicular Block

 

Injury Considerations

  • Erb’s Palsy: upper plexus injury (C5–C6).
  • Klumpke’s Palsy: lower plexus injury (C8–T1).

Positioning Precautions

  • Brachial plexus: arm abduction < 90°, avoid excessive neck stretch or compression.
  • Ulnar nerve: keep forearm neutral or supinated to reduce postcondylar groove pressure.
  • Radial nerve: avoid prolonged pressure on postcondylar groove.
  • Median nerve: avoid hyperextension of elbow.

Symptoms of injury: weakness, paresthesia, or numbness in corresponding distribution.

 

Media

 

References

License

Icon for the Creative Commons Attribution-NonCommercial 4.0 International License

The Scope Copyright © by Bailey Freeman, DNP, CRNA; Angela Mordecai, DNP, CRNA; Brian Cornelius, DNP, CRNA; and Kristin Barkley, DNP, CRNA is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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