The brachial plexus is a complex network of nerves that originates from the spinal cord and is responsible for the motor and sensory innervation of the upper limb (arm and hand). It is formed by the ventral rami (anterior branches) of spinal nerves C5, C6, C7, C8, and T1, and it can also receive contributions from C4 and T2 in some individuals.
Organization of the Brachial Plexus
The brachial plexus can be divided into several sections, which are typically organized into five parts:
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Roots: The brachial plexus begins with the five roots, corresponding to the spinal nerve roots:
- C5
- C6
- C7
- C8
- T1
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Trunks: The roots combine to form three trunks:
- Upper trunk (C5 and C6)
- Middle trunk (C7)
- Lower trunk (C8 and T1)
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Divisions: Each trunk splits into two divisions (anterior and posterior), resulting in a total of six divisions.
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Cords: The divisions regroup into three cords, named according to their position relative to the axillary artery:
- Lateral cord (formed from the anterior divisions of the upper and middle trunks)
- Posterior cord (formed from the posterior divisions of all three trunks)
- Medial cord (formed from the anterior division of the lower trunk)
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Branches: Finally, the cords give rise to several peripheral nerves that innervate the upper limb. Some of the major terminal branches include:
- Musculocutaneous nerve: Supplies muscles of the anterior compartment of the arm.
- Axillary nerve: Innervates the deltoid and teres minor muscles and provides sensation to the skin overlying the deltoid muscle.
- Radial nerve: Supplies the extensor muscles of the arm and forearm and provides sensation to the posterior arm and forearm.
- Median nerve: Innervates most of the flexor muscles in the forearm and the thenar muscles of the hand; responsible for sensation in the palmar aspect of the hand.
- Ulnar nerve: Supplies some of the forearm flexors and most intrinsic hand muscles; provides sensation to the medial aspect of the hand.
Clinical Significance
Injuries to the brachial plexus can lead to a variety of symptoms, including weakness, sensory loss, or paralysis in the arm. Common causes of brachial plexus injuries include traumatic injuries (such as motor vehicle accidents, falls, or sports injuries), as well as birth-related injuries (such as Erb’s palsy).
Understanding the anatomy and organization of the brachial plexus is essential for diagnosing and managing conditions related to the upper limb, as well as for performing regional anesthesia techniques, such as brachial plexus blocks.
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