Brachial Plexus

C5 – T1 · Nerves to the upper limb

RootsC5–T1

Trunks3

Divisions6

Cords3

Terminalbranches

Clean plexus map

Roots, trunks, divisions

Roots

Anterior rami of C5–C8 and most of T1
Receive gray rami communicantes (sympathetic fibres) near origin
Pass through posterior triangle, between anterior and middle scalene
Lie superior and posterior to subclavian artery
Branches: dorsal scapular (C5) → rhomboids; long thoracic (C5–C7) → serratus anterior

Trunks

Superior: C5 + C6
Middle: continuation of C7
Inferior: C8 + T1
Pass laterally over rib I, enter axilla
Inferior trunk lies on rib I, posterior to subclavian artery
Only branches (from upper trunk): suprascapular nerve + nerve to subclavius (both C5–C6)
Upper trunk = Erb’s point: formed by 2 nerves, ends as 2 nerves, has 2 branches

Divisions

Each trunk → 1 anterior + 1 posterior division (3 + 3 = 6)
Anterior → nerves of anterior compartments of arm and forearm
Posterior → nerves of posterior compartments
No peripheral nerves come directly from divisions

Rule of thumb

Anterior compartment nerves ← medial and lateral cords
Posterior compartment nerves ← posterior cord
Cords relate to the 2nd part of the axillary artery

Cords and their branches

Lateral cord

Anterior divisions of upper + middle trunks (C5–C7)
Lateral to axillary artery
3 nerves: lateral pectoral · musculocutaneous · lateral root of median

Medial cord

Continuation of anterior division of inferior trunk (C8, T1)
Medial to axillary artery
5 branches: medial pectoral · medial cutaneous n. of arm · medial cutaneous n. of forearm · medial root of median · ulnar

Posterior cord

Union of all 3 posterior divisions (C5–T1)
Posterior to axillary artery
5 nerves: superior subscapular · thoracodorsal · inferior subscapular · axillary · radial

“M” sign

Musculocutaneous, lateral root, median, medial root and ulnar form an M over the 3rd part of the axillary artery

Main nerves

Nerve	Cord	Key points
Musculocutaneous	Lateral	Pierces coracobrachialis; supplies coracobrachialis, biceps, brachialis; ends as lateral cutaneous n. of forearm
Median	Lateral + medial roots	Forms anterior to 3rd part of axillary artery; most anterior forearm muscles (not FCU, medial half of FDP); thenar muscles, 2 lateral lumbricals
Ulnar	Medial	FCU + medial half of FDP; all intrinsic hand muscles except thenar and 2 lateral lumbricals
Axillary	Posterior	Through quadrangular space, around surgical neck of humerus; deltoid + teres minor; superior lateral cutaneous n. of arm
Radial	Posterior	Largest terminal branch; triangular interval; all muscles of posterior arm and forearm; skin of posterior arm and forearm

Clinical

Erb’s paralysis

Superior trunk: C5, C6 roots, suprascapular n., nerve to subclavius, anterior + posterior divisions
“Waiter’s tip”: arm adducted and medially rotated, elbow extended, forearm pronated

Klumpke’s paralysis

Inferior trunk: C8, T1 roots
Claw hand: hyperextension at MCP, flexion at IP joints
May go with Horner’s syndrome

Where injury hits: cervical spinal cord injury or pulling → roots · severe trauma to 1st rib → trunks · glenohumeral dislocation → divisions and cords

Small nerves in your drawing

Nerve	From	Supplies
Dorsal scapular	Root C5	Rhomboid major + minor (C4, C5); levator scapulae also gets C3, C4 branches
Long thoracic	Roots C5–C7	Serratus anterior
Suprascapular	Upper trunk (C5, C6)	Supraspinatus, infraspinatus; through suprascapular foramen
Nerve to subclavius	Upper trunk (C5, C6)	Subclavius
Lateral pectoral	Lateral cord	Pectoralis major
Medial pectoral	Medial cord (C8, T1)	Pectoralis minor (+ part of major)
Upper subscapular	Posterior cord	Subscapularis
Lower subscapular	Posterior cord (C5–C7)	Subscapularis + teres major
Thoracodorsal	Posterior cord (C6–C8)	Latissimus dorsi
Axillary	Posterior cord (C5, C6)	Deltoid, teres minor

Check on your drawing

Lower subscapular nerve supplies teres major too (Table 2.5). Your drawing only lists subscapularis.
“Median pectoral” and “median brachial/antebrachial cutaneous” should be medial. Median is a different nerve.
The medial cutaneous nerve of the arm supplies skin of the medial arm and the axilla floor. Forearm skin (medial and posterior) belongs to the medial cutaneous nerve of the forearm. Your brachial label has forearm skin mixed in.
Everything else (roots, trunks, cords, M-sign branches) matches the book.

Myotomes and dermatomes

Movements

Shoulder abduction: C5
Elbow flexion: C6 (C5)
Elbow extension: C7
Finger flexion: C8
Finger abduction/adduction: T1

Reflexes and skin

Biceps tendon tap: C6
Triceps tendon tap: C7
Skin: C5 upper lateral arm · C6 thumb pad · C7 index pad · C8 little finger pad · T1 medial elbow

Peripheral nerve injury = loss of sensation in that nerve’s area. Spinal nerve injury = loss in a dermatome.

Who supplies what

Musculocutaneous: anterior arm; skin of anterolateral forearm
Median: anterior forearm except FCU + medial half of FDP; thenar muscles + 2 lateral lumbricals; palmar lateral 3½ digits
Ulnar: FCU, medial half FDP; most intrinsic hand muscles; medial 1½ digits
Radial: all posterior arm and forearm muscles; skin of posterior forearm and dorsolateral hand

Fig 2.16: Nerves of arm and forearm, and their skin areas

Course of the big three

Median (C5–T1)

Crosses brachial artery lateral to medial → most medial content of cubital fossa
Between 2 heads of pronator teres → between FDS and FDP → between palmaris longus and FCR tendons → carpal tunnel
Anterior interosseous nerve: FPL, lateral half FDP, pronator quadratus
Palmar branch passes over the retinaculum, so it is spared in carpal tunnel syndrome

Ulnar (C7–T1)

Pierces medial intermuscular septum → behind medial epicondyle → between 2 heads of FCU
Forearm: only FCU + medial half FDP
Enters hand superficial to retinaculum, through Guyon’s canal, lateral to pisiform
Deep branch (motor): hypothenar, interossei, adductor pollicis, 2 medial lumbricals. Superficial branch (sensory): palmaris brevis + little finger and medial half of ring finger

Radial (C5–T1)

Through triangular interval → spiral groove → pierces lateral intermuscular septum
Supplies triceps, anconeus; brachioradialis + ECRL before dividing
Superficial branch: sensory. Deep branch: motor, through supinator, becomes posterior interosseous nerve

Nerves and bone

Surgical neck → axillary nerve

Radial groove → radial nerve

Medial epicondyle → ulnar nerve

More clinical points

Anterior interosseous palsy: weak FPL + lateral FDP + pronator quadratus. Can’t make the “OK” sign
Pronator teres syndrome: median entrapment between the 2 heads or by ligament of Struthers
Cubital tunnel syndrome: ulnar entrapment between 2 heads of FCU
Wartenberg’s syndrome: superficial radial entrapment between brachioradialis and ECRL
Ulnar injury (elbow or wrist): claw hand, MCP hyperextended, IP flexed, adductor pollicis lost. Claw is worse at the wrist, because at the elbow the medial FDP is paralysed too
Dorsal branch of ulnar nerve (leaves in distal forearm): intact dorsal hand sensation → lesion at the wrist; lost → lesion more proximal

Fig 2.110: Claw hand from an ulnar nerve lesion

Spaces

Quadrangular

Teres minor, teres major, long head triceps, surgical neck. Axillary nerve + posterior circumflex humeral vessels

Triangular interval

Long head triceps, humerus shaft, teres major. Radial nerve + profunda brachii

Muscle tables (nerve and action)

Muscle	Nerve (roots)	Function
Trapezius	Accessory n. XI (motor); C3, C4 (proprioception)	Elevates, retracts, rotates scapula
Deltoid	Axillary (C5, C6)	Main abductor of arm; clavicular fibres flex, posterior fibres extend
Levator scapulae	C3, C4 + dorsal scapular (C5)	Elevates scapula
Rhomboid minor / major	Dorsal scapular (C4, C5)	Elevate and retract scapula
Supraspinatus	Suprascapular (C5, C6)	Rotator cuff; starts abduction; stabilises joint
Infraspinatus	Suprascapular (C5, C6)	Rotator cuff; lateral rotation
Teres minor	Axillary (C5, C6)	Rotator cuff; lateral rotation
Teres major	Lower subscapular (C5, C6, C7)	Medial rotation + extension of arm
Subscapularis	Upper + lower subscapular (C5, C6, C7)	Rotator cuff; medial rotation
Latissimus dorsi	Thoracodorsal (C6, C7, C8)	Adduction, medial rotation, extension
Long head of triceps	Radial (C6, C7, C8)	Extends forearm; adducts + extends arm
Pectoralis major	Medial + lateral pectoral (clavicular C5, C6; sternocostal C6–T1)	Flexion, adduction, medial rotation
Pectoralis minor	Medial pectoral (C5–T1)	Pulls scapula down + forward
Subclavius	Nerve to subclavius (C5, C6)	Pulls clavicle down + medially

Rotator cuff = SITS: Supraspinatus, Infraspinatus, Teres minor, Subscapularis. Axillary n. = deltoid + teres minor. Suprascapular = supra + infraspinatus.

More important points

Page 80 (axilla and breast)

Pectoralis major forms most of the anterior axillary wall and attaches humerus to chest wall
The breast lies over it; the axillary process extends round its lateral margin into the axilla
Lymph from the lateral and superior breast drains mainly to axillary nodes

Hand nerves (page 219–221)

Ulnar, median and radial all give skin supply; radial only supplies the dorsolateral hand
Ulnar divides just distal to the pisiform into deep (motor) and superficial (sensory) branches
Deep branch runs through Guyon’s canal between the hook of hamate and flexor tendons; ganglia can compress it
Ulnar injury sites: behind the medial epicondyle and at the wrist (lateral to pisiform)
Palm incisions: parallel to creases, longer than dorsal ones, cross flexion creases in a Z shape

Radial nerve (page 194): it supplies brachioradialis + ECRL before dividing. Deep branch supplies ECRB, passes through supinator, supplies it, then emerges as the posterior interosseous nerve for the remaining extensors.

Remember

Roots 5 (C5–T1) · Trunks 3 · Divisions 6 · Cords 3
Lateral = 3 nerves · Medial = 5 · Posterior = 5
Only trunk branches: suprascapular + nerve to subclavius (upper trunk)
Upper trunk → Erb’s · Lower trunk → Klumpke’s