Brachial Plexus

Plexus is a network of nerves or vessels in the body. The Brachial Plexus is a plexus of nerves formed by anterior/ ventral rami of lower four cervical (C_5-8) and first thoracic (T₁) spinal nerves. There may also a contribution from C₄ (Prefixed Brachial Plexus) & T₂ (Postfixed Brachial Plexus) can be seen.

Formation:

It consists of 4 components –

Roots

Located in the neck deep to Scaleneus anterior muscle
Constituted of anterior rami of C_5-8 & T₁ spinal nerves

Trunks

Located in the neck between Scaleneus anterior & Scaleneus medius muscles
Forms 3 trunks –
1. Upper Trunk by joining C₅and C₆ roots
2. Middle Trunk by C₇ root alone
3. Lower Trunk by C₈and T₁ roots

Divisions

Located behind Clavicle
Each trunk divides into 2 divisions forming total 6 divisions

Cords

Located in the Axilla
Forms 3 cords –
1. Lateral Cord by Anterior divisions of Upper and Middle trunk
2. Posterior Cord by Posterior divisions of all 3 (Upper, Middle, Lower) trunks
3. Medial Cord by Anterior division of Lower Trunk alone

Branches:

From Roots

Long Thoracic Nerve (C_5,6,7) – Serratus anterior
Dorsal Scapular Nerve (C₅) – Rhomboids

From Trunks

Suprascapular Nerve (C_5,6) – Supraspinatus & Infraspinatus
Nerve to Subclavius (C_5,6) – Subclavius

“Both originate from Upper Trunk”

From Cords

Lateral –
1. Lateral Pectoral Nerve (C_5,6,7) – Pectoralis major
2. Musculocutaneous Nerve (C_5,6,7) – Coracobrachialis, Brachialis, Biceps brachii & Skin of radial side of forearm.
3. Lateral Root of Median Nerve (C_5,6,7)
Posterior –
1. Upper Subscapular Nerve (C_5,6) – Upper part of Subscapularis
2. Thoraco-dorsal Nerve (C_6,7,8) – Latissimus dorsi
3. Lower Subscapular Nerve (C_5,6) – Lower part of Subscapularis
4. Axillary Nerve (C_5,6) – Deltoid, Teres minor & Skin of lateral shoulder and back of arm
5. Radial Nerve (C_{5,6 and}T₁)
Medial –
1. Medial Pectoral Nerve (C₈ and T₁) – Pectoralis major & Pectoralis minor
2. Medial Cutaneous Nerve of arm (T₁)
3. Medial Cutaneous Nerve of forearm (C₈ and T₁)
4. Ulnar Nerve (C_7,8 and T₁)
5. Medial Root of Median Nerve (C₈ and T₁)

Applied Anatomy:

Movements controlled by Spinal Segments –

Adduction of Shoulder – C₅
Abduction of Shoulder – C_6,7
Flexion of Elbow – C_5,6
Extension of Elbow – C_6,7
Flexion of Wrist and Fingers – C₈ T₁

Erb’s point –

The region of Upper Trunk of Brachial Plexus where 6 nerves meet –

C₅ root
C₆ root
Suprascapular Nerve from Upper Trunk
Nerve to Subclavius from Upper Trunk
Anterior division of Upper Trunk
Posterior division of Upper Trunk

Erb’s Paralysis (Upper Plexus Injury) –

Due to Hyperextension of neck (C_5,6 Injury & at Erb’s Point)
Paralysis caused –
1. Deltoid (cause Adduction of Arm)
2. Supraspinatus, Infraspinatus, Teres major (cause Medial rotation of Arm)
3. Biceps brachii (cause Extension of Elbow, Pronation of Forearm)
Loss of sensation along outer aspect of arm (C₆)
Position feature of Upper Limb – Policeman’s tip or Porter’s tip or Waiter’s tip position
Autonomic Signs absent

Klumpke’s Paralysis (Lower Plexus Injury) –

Due to Hyper Abduction of Arm (C₈and T₁)
Paralysis cause –
1. Flexors of Wrist and Fingers, Intrinsic Muscles of Hand (cause Claw hand)
Loss of sensation along medial border of forearm and hand (T₁)
Position feature of Upper Limb – Claw hand.
Autonomic signs present – Horner’s Syndrome (partial ptosis, miosis, anhydrosis and enophthalmos due to involvement of T₁ as it contains sympathetic nerves supplying head and neck)

NB: Identification in Cadaver

Find the Axillary Artery (Tube structure that doesn’t stay collapse on pinching unlike veins) at the Axillary space.

Radial Nerve (Solid cord like structure) can be identified Posteriorly to Axillary Artery running along the shaft of humerus bone.
Median Nerve can be identified Antero-laterally to Axillary Artery that also run along shaft, and bifurcates if traced backwards to origin (towards neck), which are medial and lateral roots of Median Nerve
Other Structures hence can be Identified from these by tracing backwards.