Lecture Notes: Brachial Plexus Anatomy

Introduction

• Plexus: A branching network of nerves or blood vessels.
• Brachial Plexus: A network of nerves extending from the anterior rami of cervical nerves C5 to C8 and the first thoracic root T1.

Pathway and Areas Supplied

• Pathway: Passes through the cervical axillary canal, a passageway between the scapula and clavicle bordered medially by the first rib.
• Supplied Areas: Skin and muscles of the upper limb (shoulder, arm, hand).

Sections of the Brachial Plexus

• Mnemonic: The Bear Came Down The River
  • Roots
  • Trunks
  • Divisions
  • Cords
  • Terminal Branches

Detailed Structure

Roots

• First section of a nerve leaving the CNS.
• C5 to C8 roots and T1 root: Even though there are 7 cervical vertebrae, there are 8 cervical nerves.
• Emerge through foramina in the vertebral column.

Trunks

• C5 and C6 roots: Form the Upper Trunk.
• C7 root: Continues to form the Middle Trunk.
• C8 and T1 roots: Form the Lower Trunk.

Scalene Muscles

• Located on either side of the brachial plexus, lateral to the cervical tract.

Divisions

• Each trunk splits into:
  • Anterior Division (superficial, supplies anterior upper limb)
  • Posterior Division (supplies posterior upper limb)

Cords

• Posterior Divisions: Form the Posterior Cord.
• Anterior Divisions of Upper and Middle Trunks: Form the Lateral Cord.
• Anterior Division of Lower Trunk: Continues as the Medial Cord.
• Location: Surround the axillary artery and named based on their position relative to it.
  • Posterior Cord: Posterior to the axillary artery.
  • Lateral and Medial Cords: On either side.

Terminal Branches

Posterior Cord

• Axillary Nerve: Passes through quadrangular space to innervate deltoid and teres minor; gives sensation to shoulder joint and skin over the inferior deltoid.
• Radial Nerve: Supplies posterior upper limb, innervating triceps, posterior forearm, associated joints, and overlying skin.

Lateral Cord

• Musculocutaneous Nerve: Supplies biceps brachii, brachialis, coracobrachialis; provides sensation to lateral forearm.
• Lateral Root of Median Nerve

Medial Cord

• Medial Root of Median Nerve
• Ulnar Nerve: Innervates part of the forearm and majority of the hand; sensation to medial forearm, wrist, and one and one-half fingers.

Conclusion

• Summary: 5 roots, 3 trunks, 6 divisions (3 anterior, 3 posterior), 3 cords, and 5 branches.
• Anatomical Reference: The lateral and medial roots of the median nerve, median nerve proper, musculocutaneous nerve, and ulnar nerve form an "M" shape.