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Brachial Plexus

Synonym: Plexus brachialis

German: Plexus brachialis

1 Definition

The brachial plexus is a plexus, which is formed by the anterior branches of the nerve roots C5-C8 and Th1. The nerves of arm and chest originate from here.

2 Function

The brachial plexus supplies the motor nerves of the shoulder muscles, and the motor and sensory nerves of arm and hand.

3 Structural classification

From a structural viewpoint, the brachial plexus can be roughly divided into three sections: trunks, cords and nerves originating from there.

3.1 Trunks

The trunks directly follow the anterior nerve roots of the brachial plexus. Due to their topographic situation, one distinguishes:

  • Superior trunk: Starts where nerve fibers from C5 and C6 merge
  • Medial trunk: Directly starts in the nerve fibers from C7
  • Inferior trunk: Starts where nerve fibers from C8 and Th1 merge

3.2 Cords

While progressing toward distal, each trunk forms an anterior and posterior division, which in turn forms the cords. They are characteristically positioned around the axillary artery, thus giving names to the cords according to their position to the artery. One distinguishes:

  • Lateral cord: This cord starts in the combined anterior divisions from superior trunk and medial trunk.
  • Medial cord: It starts in the anterior division of the inferior trunk.
  • Posterior cord: This cord starts in the three posterior divisions of all trunks.

3.3 Nerves

The various nerves originate in the individual cords, possibly by the combination of the different cords’ fibrous parts, and are briefly presented below:

  • Musculocutaneous nerve: It directly originates in the lateral cord and supplies motor function to the flexors of the upper arm and sensation to part of the forearm’s skin.·
  • Median nerve: It originates where fibers of the lateral and medial cords come together and innervates the motor unit of various flexors in the forearm and some hand muscles and gives sensation to the palm and parts of the fingers I-IV
  • Ulnar nerve: It originates directly in the medial cord and innervates the motor unit of various flexors in the forearm, parts of the hand muscles and sensory parts of the back of the hand, palm and fingers I-IV
  • Medial cutaneous nerve of the forearm and medial cutaneous nerve of the arm: These two nerve branches also originate in the medial cord and supply sensation to the medial side of the upper arm and forearm.
  • Axillary nerve: It originates in the posterior cord and partially innervates the motor unit of the shoulder girdle muscles and supplies sensation to the shoulder’s skin.
  • Radial nerve: This nerve also originates in the posterior cord and innervates the motor unit of all extensors in the arm and parts of the hand muscles, and supplies sensation to the dorsal side of the arm.

3.4 Additional nerves

In addition, the following nerves directly originate in the segments of the spinal cord and/or in the trunks:

4 Topographic structure

According to topography, the brachial plexus can be subdivided into two sections:

  • Supraclavicular part: Situated above the clavicle (collarbone)
  • Infraclavicular part: Situated below the clavicle

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