Overview of the Brachial Plexus

Introduction

• The brachial plexus is a network of nerves that provides motor and sensory innervation to the upper limb.
• Comprised of the spinal cord levels C5 to T1.

Structure of the Brachial Plexus

• Divisions from proximal to distal: Roots, Trunks, Divisions, Cords, and Branches.
• Mnemonic: "Randy Travis Drinks Cold Beer" or "Rugby Teams Drink Cold Beverages".

Roots

• Formed by the ventral rami of C5, C6, C7, C8, and T1.
• C5 to C8 nerve roots course above their associated vertebrae, while C8 courses below C7 vertebra and T1 courses below its vertebra.
• Branches from Roots:
  • Dorsal Scapular Nerve: Innervates levator scapulae and rhomboid muscles.
  • Long Thoracic Nerve: Innervates serratus anterior.
• Each root has associated dermatomes (skin areas) and myotomes (muscle movements).

Trunks

• Roots combine to form:
  • Upper Trunk: C5 and C6.
  • Middle Trunk: C7.
  • Lower Trunk: C8 and T1.
• Suprascapular Nerve: Branches from the upper trunk, innervates supra- and infraspinatus muscles.

Divisions

• Each trunk divides into an anterior and posterior division.
• Anterior divisions innervate flexors (ventral muscles); posterior divisions innervate extensors (dorsal muscles).
• No specific branches associated with divisions.

Cords

• Divisions give rise to three cords named relative to the axillary artery:
  • Lateral Cord
  • Medial Cord
  • Posterior Cord
• Branches from Cords:
  • Lateral Cord: Lateral pectoral nerve (innervates pectoralis major).
  • Medial Cord: Medial pectoral nerve (innervates pectoralis major and minor), medial cutaneous nerves of the arm and forearm.
  • Posterior Cord: Upper and lower subscapular nerves (innervate subscapularis), thoracodorsal nerve (innervates latissimus dorsi).

Terminal Branches

• Derived from cords:
  • Axillary Nerve: Innervates deltoid and teres minor.
  • Radial Nerve: Innervates triceps, forearm extensors, and provides cutaneous sensation to the hand's dorsal side.
  • Musculocutaneous Nerve: Innervates biceps, brachialis, and provides lateral forearm sensation.
  • Median Nerve: Innervates forearm flexors, thenar muscles, and provides sensation to the palmar side of the hand.
  • Ulnar Nerve: Innervates flexor carpi ulnaris, part of flexor digitorum profundus, and many intrinsic hand muscles.

Clinical Applications

• Interscalene Block: Anesthesia technique for brachial plexus useful for shoulder, arm, and elbow procedures.
• Sensory and motor neuron pathways are critical for diagnosing nerve damage or dysfunction.

Conclusion

• The brachial plexus is a complex nerve network essential for upper limb function, with various components each serving specific roles in motor and sensory innervation.