Brachial Plexus

Summary

The brachial plexus is a network of nerves in the shoulder that carries motor and sensory signals from the spinal cord to the arms and hands. The brachial plexus is organized into 5 sections: the roots, trunks, divisions, cords, and branches.

The roots consist of the cervical nerve roots from C5 through C8, as well as the first thoracic nerve root of T1. Notably, the long thoracic nerve originates from the C5, C6, and C7 nerve roots.

The upper, middle, and lower trunks are named according to their anatomical position.

Next, each trunk splits into anterior and posterior divisions. These divisions also form connections between the different trunks, with 2 connections going both ways between the middle and upper trunk, and only 1 connection running from the lower to the middle trunk.

Following, the divisions form 3 cords, named the lateral cord, the posterior cord, and medial cord. 

These cords then separate into nerve branches. The musculocutaneous nerve arises solely from the lateral cord, taking fibers from the C5, C6, and C7 nerve roots. The ulnar nerve arises solely from the medial cord, taking fibers from the C8 and T1 nerve roots. The median nerve arises from both the lateral and the medial cords, so it takes fibers from all the nerve roots, from C5 through T1. The radial nerve and axillary nerve both arise from the posterior cord. The radial nerve takes fibers from all the nerve roots, from C5 through T1. On the other hand, the axillary nerve is small in size, and only takes fibers from the C5 and C6 nerve roots.

Key Points

• Brachial Plexus
  • Overview
    • Network of nerves in the shoulder that carries movement and sensory signals from the spinal cord to the arms and hands
  • Sections
    • Roots
      • Spinal nerve roots of C5, C6, C7, C8, T1
        • Long thoracic nerve
          • Originates from C5, C6, C7 nerve roots
          • Innervates the serratus anterior muscle
          • Injury causes winged scapula
    • Trunks
      • Upper trunk
        • Originates from C5, C6
        • Damaged in Erb Palsy
      • Middle trunk
        • Originates from C7 only
      • Lower trunk
        • Originates from C8, T1
        • Damaged in Klumpke Palsy or Thoracic Outlet Syndrome
    • Divisions
      • Trunks split into an anterior & posterior division
    • Cords
      • Lateral cord
        • Originates from upper & middle trunks (C5, C6, C7)
      • Posterior cord
        • Originates from all trunks (C5, C6, C7, C8, T1)
      • Medial cord
        • Originates lower trunk only (C8, T1)
    • Branches
      • Musculocutaneous nerve
        • Originates from lateral cord (C5, C6, C7)
        • Innervates the biceps, brachialis, and coracobrachialis muscles
        • Provides sensory innervation to the lateral side of the forearm
      • Median nerve
        • Originates from lateral & medial cords (C5, C6, C7, C8, T1)
        • Innervates muscles and skin of the lateral part of the hand
      • Ulnar nerve
        • Originates from medial cord (C8, T1)
        • Innervates muscles and skin of the medial part of the hand
      • Radial nerve
        • Originates from posterior cord (C5, C6, C7, C8, T1)
        • Innervates the triceps, the extensors of the wrist and hand
        • Provides sensory innervation to the dorsum of the hand
      • Axillary nerve
        • Small nerve originating from posterior cord (C5, C6)
        • Innervates the deltoid, triceps, and teres minor muscles