What is the brachial plexus?

The brachial plexus is a network of ventral rami of spinal nerves C5 to T1 that provides motor, sensory, and sympathetic innervation to the upper limb.

Which spinal nerve roots form the brachial plexus?

The brachial plexus is formed by the ventral rami of C5, C6, C7, C8, and T1 spinal nerves.

What is the correct order of components of the brachial plexus?

The correct order is Roots, Trunks, Divisions, Cords, and Branches.

How many trunks are present in the brachial plexus?

There are three trunks: upper trunk (C5–C6), middle trunk (C7), and lower trunk (C8–T1).

What is the functional significance of anterior and posterior divisions?

Anterior divisions supply flexor compartments of the upper limb, while posterior divisions supply extensor compartments.

Why are the cords of the brachial plexus named lateral, medial, and posterior?

They are named according to their position relative to the second part of the axillary artery.

Which nerve is responsible for winged scapula and why?

The long thoracic nerve causes winged scapula when injured because it supplies the serratus anterior muscle.

What is Erb palsy and which nerve roots are involved?

Erb palsy is an upper trunk injury involving C5–C6 nerve roots, resulting in a waiter’s tip deformity.

What is Klumpke palsy and what are its key features?

Klumpke palsy is a lower trunk injury (C8–T1) characterized by intrinsic hand muscle paralysis, claw hand, and sometimes Horner syndrome.

Which nerve arises from all roots of the brachial plexus?

The median nerve receives fibers from all roots C5 to T1.

Which brachial plexus nerve pierces the coracobrachialis muscle?

The musculocutaneous nerve pierces the coracobrachialis muscle.

Which nerve injury causes wrist drop?

Radial nerve injury causes wrist drop due to paralysis of wrist extensors.

What is thoracic outlet syndrome in relation to the brachial plexus?

Thoracic outlet syndrome involves compression of the lower trunk of the brachial plexus as it passes between the clavicle and first rib.

Which cord gives rise to the ulnar nerve?

The ulnar nerve arises from the medial cord of the brachial plexus.

Why is the brachial plexus clinically important?

It is crucial because injuries at different levels produce characteristic motor and sensory deficits, aiding localization of nerve damage.

Brachial Plexus Anatomy Explained with Roots Trunks Cords Branches and Clinical Correlations

Brachial Plexus – Complete Detailed Anatomy

Definition

The brachial plexus is a network of ventral rami of spinal nerves C5–T1 that provides motor, sensory, and sympathetic innervation to the upper limb.

Formation (Roots → Trunks → Divisions → Cords → Branches)

1. Roots

C5, C6, C7, C8, T1 (ventral rami)
Pass between anterior and middle scalene muscles in the neck
Branches from roots:

* Dorsal scapular nerve (C5) → Rhomboids, levator scapulae

* Long thoracic nerve (C5–C7) → Serratus anterior (winged scapula if injured)

2. Trunks

Formed in the posterior triangle of the neck

Upper trunk: C5–C6
Middle trunk: C7
Lower trunk: C8–T1

Branches from trunks:

Suprascapular nerve (C5–C6) → Supraspinatus, infraspinatus
Nerve to subclavius (C5–C6)

3. Divisions

Located behind the clavicle

Each trunk divides into:

* Anterior division → Flexor compartments

* Posterior division → Extensor compartments

No branches arise here

4. Cords

Named according to relation to the axillary artery (in axilla)

| Cord | Formation |

| ------------------ | ------------------------------------------- |

| Lateral cord | Anterior divisions of upper + middle trunks |

| Medial cord | Anterior division of lower trunk |

| Posterior cord | All posterior divisions |

5. Terminal Branches

From Lateral Cord

Musculocutaneous nerve (C5–C7)
Lateral root of median nerve

From Medial Cord

Ulnar nerve (C8–T1)
Medial root of median nerve
Medial cutaneous nerve of arm
Medial cutaneous nerve of forearm

From Posterior Cord

Axillary nerve (C5–C6)
Radial nerve (C5–T1)

Major Peripheral Nerves – Functions & Lesions

Musculocutaneous Nerve (C5–C7)

Motor: Biceps, brachialis, coracobrachialis
Sensory: Lateral forearm
Injury: Weak elbow flexion & supination

Axillary Nerve (C5–C6)

Motor: Deltoid, teres minor
Sensory: Regimental badge area
Injury: Surgical neck fracture → loss of shoulder abduction (15–90°)

Radial Nerve (C5–T1)

Motor: All extensors of arm & forearm
Sensory: Posterior arm, forearm, dorsal hand
Injury: Wrist drop

Median Nerve (C5–T1)

Motor: Forearm flexors, thenar muscles
Sensory: Lateral 3½ digits (palmar)
Injury: Ape hand, loss of pronation, carpal tunnel syndrome

Ulnar Nerve (C8–T1)

Motor: Intrinsic hand muscles
Sensory: Medial 1½ fingers
Injury: Claw hand, Froment sign

Clinical Correlations

Upper Trunk Lesion (Erb Palsy – C5–C6)

Causes: Birth injury, fall on shoulder
Deformity: “Waiter’s tip”
Affected nerves: Axillary, musculocutaneous, suprascapular

Lower Trunk Lesion (Klumpke Palsy – C8–T1)

Causes: Traction of abducted arm
Features:

* Intrinsic hand muscle paralysis

* Claw hand

* Horner syndrome (if T1 sympathetic affected)

Applied Anatomy

Scalene block anesthesia targets roots/trunks
Axillary block targets terminal branches
Thoracic outlet syndrome affects lower trunk
Winged scapula → Long thoracic nerve injury

Key Exam Mnemonic

Roots → Trunks → Divisions → Cords → Branches

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