What nerves arise from the lateral cord, posterior cord, and middle cord of the brachial plexus?

Nerves Arising from the Brachial Plexus Cords

The lateral cord gives rise to the musculocutaneous nerve and the lateral root of the median nerve; the medial cord gives rise to the ulnar nerve and the medial root of the median nerve; and the posterior cord gives rise to the axillary nerve and the radial nerve 1.

Note: There is no "middle cord" in the brachial plexus anatomy—the three cords are lateral, medial, and posterior 2, 1.

Lateral Cord Branches

• Musculocutaneous nerve: Terminal branch that innervates the anterior compartment of the arm 1
• Lateral root of the median nerve: Joins with the medial root from the medial cord to form the median nerve 1

Medial Cord Branches

• Ulnar nerve: Terminal branch that continues into the forearm and hand 1
• Medial root of the median nerve: Combines with the lateral root to complete the median nerve formation 1

Posterior Cord Branches

• Axillary nerve: Terminal branch that innervates the deltoid and teres minor muscles 1
• Radial nerve: Terminal branch that supplies the posterior compartment of the arm and forearm 1

Anatomical Framework

The brachial plexus is formed from C5-T1 ventral rami and can be conceptualized as "five to three to three to five": five nerve roots form three trunks, which divide into three cords (lateral, medial, and posterior), which ultimately give rise to five major terminal nerves 2, 1.

Common Pitfalls

• Terminology confusion: The term "middle cord" does not exist in standard brachial plexus anatomy; the middle trunk exists at the trunk level (formed by C7 alone), but at the cord level, only lateral, medial, and posterior cords are present 1
• Anatomical variations: The posterior cord can occasionally be formed by different combinations of divisions, and terminal branches may show variations in their origin patterns 3
• Clinical significance: Understanding cord anatomy is essential for interpreting plexopathy patterns, as complete plexopathy causes weakness, sensory loss, and flaccid loss of tendon reflexes in regions innervated by nerves in the C5-T1 distribution 2