Summarize the divisions and cords of the brachial plexus, including their main branches.

Here is a summary of the information provided about the brachial plexus:

• Divisions: Within the posterior triangle of the neck, each trunk of the brachial plexus divides into two branches: an anterior division and a posterior division. The anterior divisions generally supply flexor muscles, while the posterior divisions generally supply extensor muscles. These divisions then leave the posterior triangle and pass into the axilla region.

• Cords: Once the anterior and posterior divisions have entered the axilla, they combine to form three main cords, named according to their relationship to the axillary artery:

  1. The Lateral Cord: Formed by the anterior divisions of the upper and middle trunks.
  2. The Posterior Cord: Formed by the posterior divisions of all three trunks (upper, middle, and lower).
  3. The Medial Cord: Formed by the anterior division of the lower trunk.

  These cords then give rise to the major terminal branches of the brachial plexus:

  • Lateral Cord Branches:
    • Lateral pectoral nerve
    • Musculocutaneous nerve
    • Lateral root of the median nerve
  • Posterior Cord Branches:
    • Upper subscapular nerve
    • Lower subscapular nerve
    • Thoracodorsal nerve
    • Axillary nerve
    • Radial nerve
  • Medial Cord Branches:
    • Medial pectoral nerve
    • Medial cutaneous nerve of the arm
    • Medial cutaneous nerve of the forearm
    • Medial root of the median nerve
    • Ulnar nerve