Brachial Plexus Simplified

Remember the mnemonic: Randy Travis Drinks Cold Beer.

From proximal to distal, brachial plexus consists of:

  1. Roots (C5-T1)
  2. Trunks (Upper, Middle and Lower)
  3. Divisions (Anterior and Posterior from each of 3 trunks)
  4. Cords (Lateral, Posterior and Medial)
  5. Branches

Divisions are formed behind the clavicle. Hence –

  • Roots and Trunks are Supraclavicular
  • Cords and Branches are Infraclavicular

brachial plexus

Roots

Roots enter the neck between Anterior and Medial scalene.

2 nerves arise from the root – that supplies muscles with attachment to medial border of scapula:

  1. Serratus anterior: Long thoracic nerve (C5, C6 and C7)
  2. Rhomboids: Dorsal scapular nerve (C5)

Trunks

Trunks enter the apex of axilla through the Cervico-axillary canal (clavicle anteriorly, scapula posteriorly and 1st rib medially).

2 nerves arise from the superior trunk – that supplies muscles with attachment to medial aspect of dorsal scapula or clavicle:

  1. Supraspinatus and Infraspinatus: Suprascapular nerve (C5, C6)
  2. Subclavius: Nerve to subclavius (C5, C6)

Roots and Trunks lie lateral to the 1st part of axillary artery.

Divisions

Divisions form behind the clavicle in Cervico-axillary canal.

  • No nerves arise from the divisions.

Brachial plexus relations and course

Cords

  • Posterior divisions of all 3 trunks = Posterior cord
  • Anterior division of upper and middle trunk = Lateral cord
  • Anterior division of lower trunk = Medial cord

Cords form around the 2nd part of axillary artery and are named in relation to it.

Gives 5 small nerves to the muscles with attachment to biccipital groove of humerus (remember the mnemonic Lady between 2 Majors) and lesser tubercle (only 1 rotator cuff muscle attaches to lesser tubercle of humerus).

  • From lateral and medial cord: Nerves to Pectoralis major
    • Lateral pectoral nerve (C5, C6, C7) – from lateral cord
    • Medial pectoral nerve (C8, T1) – from medial cord (also supplies pectoralis minor)
  • From posterior cord:
    • Latissimus dorsi: Thoracodorsal or Middle subscapular nerve
    • Teres major: Lower subscapular nerve (C5, C6) – from posterior cord
    • Subscapularis (rotator cuff attaching to lesser tuberosity): Upper and lower subscapular nerve (C5,C6)

Medial cord gives 2 small sensory nerves to medial aspect of upper limb:

  • Medial cutaneous nerve of arm (T1)
  • Medial cutaneous nerve of forearm (C8, T1)

Other cutaneous innervation of arm, forearm and hand:

  1. Superior lateral cutaneous nerve of arm: Axillary nerve
  2. Inferior lateral cutaneous nerve of arm, Posterior cutaneous nerve of arm and forearm, Lateral 2 and 1/2 of dorsal hand and fingers: Radial nerve
  3. Lateral cutaneous nerve of forearm: Musculocutaneous nerve
  4. Medial 1 and 1/2 of palm and fingers and Medial 2 and 1/2 of dorsal hand and fingers: Ulnar nerve
  5. Lateral 3 and 1/2 of palm and fingers and tips of lateral 3 and 1/2 fingers on dorsal hand: Median nerve

Branches

Posterior cord

1. Axillary (C5, C6) nerve passes through Quadrangular space (along with posterior circumflex humeral artery) – supplies:

  • Deltoid (from Deep Branch)
  • Teres minor (from Superficial Branch)
  • Regimental badge skin (Superior lateral cutaneous nerve)

2. Radial nerve (C5, C6, C7, C8, T1) passes through Triangular space (along with profunda brachii artery) – supplies BEAST muscles.

  • Brachioradialis
  • Extensors of forearm
  • Anconeus
  • Supinator
  • Triceps Brachii

Between the humerus and 2 Teres muscles (major and minor) anchoring it to the scapular forms a triangular space, which is further partitioned by long head of triceps) into two – lateral quadrangular and medial triangular space. Remember the 4 “T”s – Trunk (Shaft) of humerus, Teres major, Teres minor and Triceps (long head).

Remember: Teres minor is a rotator cuff muscle, not the teres major.

Lateral cord

Musculocutaneous nerve (C5, C6, C7): pierces coracobrachialis and innervates the anterior compartment of arm

  • Coracobrachialis
  • Biceps brachii

Medial cord

Ulnar nerve (C7, C8, T1)

Median nerve (C5, C6, C7, C8, T1)

  • Formed by combination of lateral and medial roots from lateral and medial cords respectively.
  • Continues down the arm lateral to the brachial artery.

Median nerve vs Ulnar nerve

Median nerve and Ulnar nerve have comparable similarities and differences that makes them easier to remember:

Median nerveUlnar nerve
Course
In armLateral to brachial artery – later crosses from lateral to medial

Parallel and anterior to medial intermuscular septum

No branches

Medial to brachial artery

 

Pierces the medial intermuscular septum

No branches

In cubital fossaAnterior to medial epicondyle – medial to biceps tendonPosterior to medial epicondyle
Enters forearmBetween two heads of pronator teresBetween two heads of flexor carpi ulnaris
In forearmLateral to ulnar arteryMedial to ulnar artery
In wristUnder flexor retinaculum – through Carpal tunnelAbove flexor retinaculum – through Guyon’s canal
Innervation
Flexor digitorum profundus (FDP)Lateral halfMedial half
Other muscles of anterior compartment of forearmRemaining muscles except flexor carpi ulnarisFlexor carpi ulnaris
Eminence group musclesThenar (Pollicis muscle group) except Adductor Pollicis

Median nerve supplies LOAF muscles.

·         Lumbricals

·         Opponens pollicis

·         Abductor pollicis brevis

·         Flexor pollicis brevis

 

The longus portion of abductor pollicis and flexor pollicis are supplied in forearm by Posterior Interosseous Nerve or PIN (branch of radial nerve) and Anterior Interosseous nerve or AIN (branch of Median nerve) respectively.

Hypothenar

Adductor Pollicis

Lumbricals2 (1st and 2nd)(3rd and 4th)
PalmarisLongusBrevis
InterosseiNoneAll (Palmar and Dorsal)
Muscles of hand2 lumbricals and thenar groupAll except those supplied by median nerve

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