Brachial plexus

The brachial plexus is a group of nerves. It runs from the vertebral column to the arm.

The right brachial plexus with its short branches, viewed from in front.

Structure

The brachial plexus is divided into five roots, three trunks, six divisions, three cords, and five branches.

Roots

The five roots come out of the spinal cord. They are each named after the part of the spinal cord they come out of: C5, C6, C7, C8, and T1.

Trunks

These roots join to form three trunks:

  • "upper" (C5-C6)
  • "middle" (C7)
  • "lower" (C8-T1)

Divisions

Each trunk then splits into two divisions:

  • anterior (front) divisions of the upper, middle, and lower trunks
  • posterior (back) divisions of the upper, middle, and lower trunks

Cords

These six divisions join up again to become the three cords.

  • The posterior cord is formed from the three posterior divisions of the trunks (C5-C8,T1)
  • The lateral cord is formed from the anterior divisions of the upper and middle trunks (C5-C7)
  • The medial cord is simply a continuation of the anterior division of the lower trunk (C8,T1)

Diagram
Drawing of the brachial plexus using colour to show where all the different nerves come from
The brachial plexus

Nerves

The nerves that come out of the brachial plexus include:

  • Radial nerve
  • Axillary nerve
  • Musculocutaneous nerve
  • Median nerve
  • Ulnar nerve
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