Nerve network supplying the upper limb. Formed by anterior primary rami of C5, C6, C7, C8, T1.

Sequence: Roots → Trunks → Divisions → Cords → Branches Memory: Really Tired Drink Coffee Now

Formation

Components of the Plexus

Trunks

Cords (named by relation to 2nd part of axillary artery)

Memory: Lateral gets 2, medial gets 1, posterior gets all 3

Parts and Relations

• Supraclavicular part: roots and trunks (posterior triangle of neck)
• Infraclavicular part: divisions, cords, branches (axilla, enclosed in axillary sheath derived from prevertebral fascia)

Branches of the Brachial Plexus

Branches from Roots

Long thoracic nerve injury: winging of scapula; loss of pushing/punching; cannot raise arm above 90°

Branches from Trunks

Only upper trunk gives named branches:

Middle and lower trunks: no named branches

Erb’s Point

Region of upper trunk where six structures meet: C5 root, C6 root, upper trunk, suprascapular nerve, nerve to subclavius, anterior + posterior divisions of upper trunk → injury here = Erb’s paralysis

Branches from Cords

Lateral cord (LMM):

Medial cord (MMMMU):

Posterior cord (ULTRA):

Terminal Nerves

Memory (lateral → medial around axillary artery): MARMU — Musculocutaneous, Axillary, Radial, Median, Ulnar

Segmental Innervation of the Upper Limb

Rule: C5–C6 = shoulder/elbow; C6–C7 = wrist; C7–C8 = fingers; T1 = intrinsics

Reflexes

Dermatomes

Applied Anatomy

Erb’s Paralysis

Upper trunk injury — C5, C6

Causes: Angle between head and shoulder forcibly increased — fall on shoulder; birth injury (traction on head/neck); sudden shoulder depression + opposite neck flexion

Paralysed muscles: Deltoid, supraspinatus, infraspinatus, teres minor, biceps brachii, brachialis, brachioradialis, supinator

Deformity: Waiter’s Tip / Policeman’s Tip

Sensory loss: lateral arm and forearm. Biceps + supinator jerks lost. No autonomic signs (T1 spared).

Klumpke’s Paralysis

Lower trunk injury — C8, T1

Causes: Excessive upward traction on limb — grasping while falling; birth injury with arm above head; arm pulled forcefully upwards

Effects:

• Paralysis of intrinsic muscles of hand
• Weakness of finger flexors (C8)
• Sensory loss along medial forearm and medial hand
• Claw hand (all fingers if lower trunk interrupts both median + ulnar T1 fibres)

Horner’s Syndrome (if T1 sympathetic fibres involved proximally):

Memory: SAME — Anhydrosis, Miosis, Enophthalmos (+ ptosis)

Erb’s vs Klumpke’s Paralysis

Thoracic Outlet / Cervical Rib

Compresses lower trunk (C8, T1) + subclavian vessels:

• Pain + paraesthesia along medial forearm and hand
• Wasting of intrinsic hand muscles
• Vascular symptoms (coldness, pallor, diminished pulse)

Axillary Surgery — Nerves at Risk

Note: Intercostobrachial nerve = lateral cutaneous branch of 2nd intercostal nerve, not a brachial plexus branch.

Quick Lesion Localisation

Rapid Revision Table

The brachial plexus is the nerve network that supplies the upper limb. It is formed by the anterior primary rami of C5, C6, C7, C8, and T1, and is organised in the sequence:

Roots → Trunks → Divisions → Cords → Branches

Memory aid: Really Tired Drink Coffee Now.

For university exams, learn it in three layers:

1. Formation and relations
2. Branches and terminal nerves
3. Lesions and segmental localisation

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Formation

The brachial plexus is formed by the anterior primary rami of the lower four cervical nerves and the first thoracic nerve:

C5 + C6 + C7 + C8 + T1

Occasional anatomical variations:

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Components of the Plexus

Roots

The five roots are the anterior primary rami of C5 to T1. They emerge in the interval between:

• Scalenus anterior anteriorly
• Scalenus medius posteriorly

They lie in the lower part of the posterior triangle and pass towards the first rib.

Trunks

Memory: C5-C6 upper, C7 middle, C8-T1 lower.

Divisions

Each trunk divides into:

• Anterior division: mainly supplies flexor/anterior compartments
• Posterior division: mainly supplies extensor/posterior compartments

Thus, there are six divisions in total. They lie behind the clavicle.

Cords

The cords are named according to their relationship to the second part of the axillary artery.

Memory: Lateral gets 2, medial gets 1, posterior gets all 3.

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Parts and Relations

The brachial plexus has:

• A supraclavicular part: roots and trunks
• An infraclavicular part: divisions, cords, and branches

Supraclavicular Part

The roots and trunks lie in the posterior triangle of the neck.

Important relations:

The plexus and subclavian artery pass between scalenus anterior and scalenus medius, while the subclavian vein lies anterior to scalenus anterior.

Infraclavicular Part

The cords and branches lie in the axilla and are enclosed with the axillary artery in the axillary sheath, which is derived from the prevertebral fascia.

Relation to axillary artery:

This relationship is important for axillary brachial plexus block.

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Branches of the Brachial Plexus

Branches are best remembered by their level of origin.

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Branches from Roots

Long Thoracic Nerve

The long thoracic nerve descends on the lateral surface of serratus anterior. It is vulnerable during axillary surgery.

Injury causes:

• Winging of scapula
• Loss of pushing/punching action
• Difficulty raising the arm above 90 degrees because serratus anterior is needed for upward rotation of the scapula

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Branches from Trunks

Only the upper trunk gives named branches.

The middle and lower trunks give no named branches.

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Erb’s Point

Erb’s point is the region of the upper trunk where six structures meet:

1. C5 root
2. C6 root
3. Upper trunk
4. Suprascapular nerve
5. Nerve to subclavius
6. Anterior and posterior divisions of the upper trunk

Injury here produces Erb’s paralysis.

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Branches from Cords

Lateral Cord

Memory: Lateral cord = LMM

Medial Cord

Memory: Medial cord = MMMMU

Posterior Cord

Memory: ULTRA

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Terminal Nerves

The five major terminal nerves are:

Memory from lateral to medial around the axillary artery: MARMU

Musculocutaneous, Axillary, Radial, Median, Ulnar

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Terminal Nerves — Exam Overview

Musculocutaneous Nerve

• Pierces coracobrachialis
• Runs between biceps brachii and brachialis
• Supplies coracobrachialis, biceps brachii, and brachialis
• Continues as the lateral cutaneous nerve of forearm
• Injury causes weak elbow flexion and weak supination

Axillary Nerve

• Passes through the quadrangular space
• Winds around the surgical neck of humerus with posterior circumflex humeral vessels
• Supplies deltoid and teres minor
• Gives upper lateral cutaneous nerve of arm to the regimental badge area
• Injury occurs in shoulder dislocation or fracture of surgical neck of humerus

Radial Nerve

• Largest branch of the brachial plexus
• Supplies all muscles of posterior compartment of arm and forearm
• Runs in the radial groove with profunda brachii artery
• Injury causes wrist drop
• Autonomous sensory area: first dorsal web space

Median Nerve

• Formed by lateral and medial roots from lateral and medial cords
• Has no branches in the arm
• Supplies most forearm flexors except flexor carpi ulnaris and medial half of flexor digitorum profundus
• Supplies LOAF muscles in the hand:
  • Lumbricals 1 and 2
  • Opponens pollicis
  • Abductor pollicis brevis
  • Flexor pollicis brevis, superficial head
• Compression in carpal tunnel causes paraesthesia in lateral 3.5 digits with sparing of thenar skin

Ulnar Nerve

• Runs behind the medial epicondyle
• Has no branches in the arm
• Supplies flexor carpi ulnaris and medial half of flexor digitorum profundus
• Supplies all intrinsic hand muscles except LOAF
• Injury causes ulnar clawing and positive Froment’s sign

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Segmental Innervation of the Upper Limb

Segmental values help localise root lesions.

Memory rule:

• C5-C6: shoulder and elbow
• C6-C7: wrist
• C7-C8: fingers
• T1: intrinsic hand muscles

Reflexes

Dermatomes

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Applied Anatomy

Erb’s Paralysis

Erb’s paralysis is an upper trunk injury involving mainly C5 and C6.

Causes

The injury occurs when the angle between the head and shoulder is forcibly increased:

• Fall on the shoulder
• Birth injury due to traction on the head and neck
• Sudden depression of shoulder with opposite flexion of neck

Paralysed Muscles

Mainly muscles supplied by C5 and C6:

• Deltoid
• Supraspinatus
• Infraspinatus
• Teres minor
• Biceps brachii
• Brachialis
• Brachioradialis
• Supinator

Deformity: Waiter’s Tip / Policeman’s Tip

Sensory loss is usually over the lateral aspect of the arm and forearm. Biceps and supinator jerks are lost. Autonomic signs are absent because T1 is spared.

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Klumpke’s Paralysis

Klumpke’s paralysis is a lower trunk injury involving mainly C8 and T1.

Causes

It occurs due to excessive upward traction on the limb:

• Grasping an object while falling from a height
• Birth injury with arm extended above the head
• Arm pulled forcefully upwards

Effects

• Paralysis of intrinsic muscles of the hand
• Weakness of finger flexors supplied by C8
• Sensory loss along medial forearm and medial hand
• Claw hand, often affecting all fingers if the lower trunk lesion interrupts both median and ulnar T1 fibres

Horner’s Syndrome

If T1 sympathetic fibres are involved proximally, Horner’s syndrome may occur:

Mnemonic: SAME — sympathetic lesion causes Anhydrosis, Miosis, Enophthalmos, with ptosis.

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Erb’s vs Klumpke’s Paralysis

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Complete Brachial Plexus Injury

Complete plexus injury involves C5 to T1.

Features:

• Complete motor paralysis of upper limb below lesion
• Widespread sensory loss
• Loss of reflexes
• Severe functional disability
• Possible autonomic changes if T1 fibres are involved

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Thoracic Outlet and Cervical Rib

A cervical rib or fibrous band may compress the lower trunk of the brachial plexus and subclavian vessels.

Features:

• Pain and paraesthesia along medial forearm and hand
• Weakness or wasting of intrinsic hand muscles
• Vascular symptoms such as coldness, pallor, or diminished pulse

This produces a lower plexus pattern because C8 and T1 are most vulnerable.

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Axillary Surgery: Nerves at Risk

During axillary lymph node dissection, important nerves at risk include:

The intercostobrachial nerve is not a branch of the brachial plexus; it is the lateral cutaneous branch of the second intercostal nerve.

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Quick Lesion Localisation

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Rapid Revision Table

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