Brachial plexus

The brachial plexus is an arrangement of nervous fibres running from the spine (vertebrae C5-T1) through the axilla (armpit region) and into the arm.

The brachial plexus starts from the five ventral rami of the spinal nerves, these are the five roots. These roots merge to form three trunks.

Each trunk then splits to form an anterior and a posterior division. These six divisions will regroup to become the cords. The cords are named by their position in respect to the axillary artery.

• The posterior cord is formed from the three posterior divisions of the trunks.
• The lateral cord is the anterior divisions from the upper and middle trunks.
• The medial cord is simply a continuation of the lower trunk.

From the cords come the nerves of the arm.

• The axillary nerve is a branch off the posterior cord, which then becomes the radial nerve.
• Branches from the lateral and medial cord from the medial nerve.
• The musculocutaneous nerve is a the rest of the lateral cord.
• And the ulnar nerve is the rest of the medial cord.