The brachial plexus and innervation of the upper extremities are some of the first topics covered in the first year of medical school. Despite early exposure, physicians regularly rely on reference materials to refresh their memories. Unfortunately, Shelf, RITE*, and Board exams will not let you forget this material. In this chapter, we will discuss the basics of the brachial plexus and upper extremity nerves. Additionally, we will cover commonly seen brachial plexopathies and upper extremity neuropathies.

Authors: Brian Hanrahan MD, Parneet Grewal MD

The brachial plexus and innervation of the upper extremities are some of the first topics covered in the first year of medical school. Despite early exposure, physicians regularly rely on reference materials to refresh their memories. Unfortunately, Shelf, RITE*, and Board exams will not let you forget this material. In this chapter, we will discuss the basics of the brachial plexus and upper extremity nerves. Additionally, we will cover commonly seen brachial plexopathies and upper extremity neuropathies.

Authors: Brian Hanrahan MD, Parneet Grewal MD

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Table of Contents

Table of Contents

Brachial Plexus

  • The brachial plexus is a network of nerve fibers that innervate muscles and provide sensation from the upper limbs.
Figure 1: Diagram of the Brachial Plexus
By Chris Talbot – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=22561787
  • It is formed by the anterior rami of cervical spinal roots C5, C6, C7, C8, and T1.
  • There are 5 sections of the brachial plexus; roots, trunks, divisions, cords, and lastly branches.
  • Branches can be considered minor branches or terminal branches (see tables below).
  • Anterior (motor) and posterior (sensory) rami contribute to the brachial plexus
  • Once leaving the intervertebral foramina, roots merge to form three trunks in the neck.
  • Upper trunk (C5-C6)
  • Middle trunk (C7)
  • Lower trunk (C8-T1)
  • Each trunk splits into anterior and posterior divisions.
  • Anterior divisions innervate flexor groups.
  • Posterior divisions innervate extensor groups.
  • Six divisions regroup to become three cords.
  • Lateral cord (C5-C7) is formed from the anterior divisions of the upper and middle trunks.
  • Medial cord (C8, T1) is the anterior division of the lower trunk.
  • Posterior cord (C5-T1) is formed from the posterior divisions of all three trunks.
  • Cords then terminate into terminal branches.
  • Branches of roots
    • Dorsal scapular nerve
    • Long thoracic nerve
  • Branches of trunks
    • Suprascapular nerve
  • Branches of the lateral cord
    • Median nerve
    • Musculocutaneous
    • Lateral pectoral nerve
    • Lateral cutaneous nerve of the forearm
  • Branches of the medial cord
    • Median nerve
    • Ulnar nerve
    • Medial pectoral nerve
    • Medial cutaneous nerve of the arm
    • Medial cutaneous nerve of the forearm
  • Branches of the posterior cord
    • Radial nerve
    • Axillary nerve
    • Thoracodorsal nerve
    • Subscapular nerve
Tip: There are many mnemonics for remembering the brachial plexus. Here are some we like!
Randy Travis Drinks Cold Beers
Read That Damn Cadaver Book
Really Tired, Don’t Care Now (nerve instead of branch)

Table 1: Minor branches of the brachial plexus

Nerve (associated nerve root) Muscle(s) and function
Dorsal Scapular nerve (C4-C5) Rhomboids: Elevation and adduction of scapula
Levator scapulae: Elevation and medial rotation of scapula
Subclavian nerve (C5-C6) Subclavian: Depression of the clavicle and elevation of first rib
Long thoracic nerve (C5-C7) Serratus anterior: Stabilization of scapula against chest wall
Suprascapular nerve (C5-C6) Supraspinatus: Shoulder abduction (first 15 degrees)
Infraspinatus: External rotation of arm
Subscapular nerves (C5-C7) Upper → Subscapularis: Internal rotation of arm
Lower → Teres Major: Adduction and internal rotation of arm
Thoracodorsal nerve (C6-C8) Latissimus dorsi: Adduction and internal rotation of arm

  • The rhomboids are solely innervated by the C5 nerve root, This can help differentiate C5 from C6 radiculopathies.

Table 2: Terminal branches of the brachial plexus

Nerve (associated nerve root) Muscle(s) and function
Axillary nerve (C5-C6) Deltoid: 15-90 degrees of shoulder abduction
Teres minor: Lateral rotation of arm
Musculocutaneous nerve (C5-C7) Biceps: Elbow flexion and forearm supination
Coracobrachialis: Elbow flexion and adduction of arm
Brachialis*: Elbow flexion
Median nerve (C5-T1) Pronator teres: Pronation of forearm
Flexor carpi radialis: Radial flexion of wrist
Palmaris longus: Flexion of wrist
Flexor digitorum superficialis: Flexion of fingers
Flexor pollicis longusª: Flexion of terminal phalanx of thumb
Flexor pollicis brevis*: Flexion at proximal phalanx of thumb
Flexor digitorum profundus I & IIª: Flexion terminal phalanx of 2,3 fingers
Pronator quadratusª: Pronation of forearm
Abductor pollicis brevis: Abduction of thumb metacarpal
Opponens pollicis: Opposition of thumb metacarpal
Lumbricals I & II: Flexion of MCP joints and extension of interphalangeal joints
Ulnar nerve (C7-T1) Flexor carpi ulnaris: Ulnar flexion of wrist
Flexor digitorum profundus: Flexion of hand and fingers
Abductor digiti minimi: Abduction of 5th digit
Opponens digiti minimi: Opposition of 5th digit
Flexor digiti minimi: Flexion of 5th digit
Lumbricals III & IV: Flexion of MCP joints and extension of interphalangeal joints
Interosseous muscles: Abduction and adduction of fingers
Adductor pollicis: Adduction of MCP joint of thumb
Flexor pollicis brevis**: Flexion at proximal phalanx of thumb
Radial nerve (C5-C8) Triceps: Extension of forearm
Anconeus: Extension of forearm
Brachialis*: Flexion of elbow
Brachioradialis: Flexion of elbow
Extensor carpi radialis longus: Radial extension of wrist
Supinator: Supination of forearm
Extensor carpi radialis brevis: Radial extension at the wrist
Extensor digitorum: Extensor of MCP joint of 2nd-5th digits
Extensor digiti minimi: Extension of MCP joint of 5th digit
Extensor carpi ulnaris: Ulnar extension of wrist
Abductor pollicis longus: Abduction of MCP of thumb
Extensor pollicis longus: Extensor of thumb
Extensor pollicis brevis: Extensor of thumb
Extensor indicis: Extension of 2nd finger

MCP: metacarpophalangeal joint, ªInnervated by the anterior interosseous nerve, *Brachialis is innervated by both the musculocutaneous and radial nerves, **Flexor pollicis brevis is innervated by both the medial and ulnar nerves.

Brachial Plexus Syndromes



 

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