Neurology of the Upper Limb

Neurology of the Upper Limb

• The spinal nerves that innervate the upper limb are C5-T1.
• The brachial plexus is formed by the anterior rami of C5-T1.
• The brachial plexus is one of the somatic plexuses.

Organization of the Spinal Nerves

• A spinal nerve consists of a dorsal root and a ventral root.
• The dorsal root ganglion contains cell bodies of sensory neurons.
• The posterior ramus innervates the back muscles, while the anterior ramus innervates the limbs.
• The sympathetic chain ganglion is located near the posterior ramus.

Dermatomes and Myotomes of the Upper Limb

• C5 innervates the upper lateral arm.
• C6-8 innervates the lateral forearm.
• C7/8 innervates the medial forearm.
• T1 innervates the medial arm.

The Axilla and the Organization of the Brachial Plexus

• The axilla is a pyramidal space with an apex (cervico-axillary inlet) and a base (axillary fossa).
• The axilla is bounded by the pectoralis major and minor, serratus anterior, ribcage, subscapularis, teres major, latissimus dorsi, and long head of triceps brachii.
• The brachial plexus is organized into roots, trunks, divisions, and cords.

The Major Terminal Branches of the Brachial Plexus

• The axillary nerve is a branch of the posterior cord of the brachial plexus (C5, C6).
• The axillary nerve exits the axilla through the quadrangular space and innervates the deltoid and teres minor.
• The musculocutaneous nerve is a branch of the lateral cord (C5-7) and pierces the coracobrachialis.
• The musculocutaneous nerve provides motor innervation to the anterior compartment of the arm (flexors) and continues as the lateral cutaneous nerve of the forearm.
• The median nerve is formed by the lateral and medial cords (C6-T1) and provides motor innervation to the muscles of the anterior forearm and hand.
• The ulnar nerve is formed by the medial cord (C8, T1) and provides motor innervation to the FCU and medial ½ FDP and hand.
• The radial nerve is formed by the posterior cord (C5-T1) and provides motor innervation to the posterior compartment of the arm and forearm (extensors).

Sites of Nerve Injuries

• The axillary nerve can be injured in shoulder dislocations, leading to loss of abduction and weakened flexion, extension, and rotation.
• The musculocutaneous nerve can be injured due to muscular compression or stretch, leading to reduced and tingling sensation in the lateral skin of the forearm.
• The median nerve can be injured in the carpal tunnel, leading to weakness of wrist flexion and loss of forearm pronation.
• The ulnar nerve can be injured in the cubital tunnel, leading to claw hand deformity.
• The radial nerve can be injured in the axilla or forearm, leading to weakness of forearm extension and wrist drop.

Recommended Reading and Watching

• Drake et al. (2015) Gray’s Anatomy for Students, Chapter 7
• Moore et al. (2014) Essential Clinical Anatomy, Chapter 6
• Acland’s Anatomy videos:
  • 1.1.11 Landmark structures for nerves and blood vessels
  • 1.1.14 Nerves of the shoulder region: the brachial plexus
  • 1.2.12 Nerves of the arm
  • 1.3.18 Radial nerve in the forearm and hand
  • 1.3.19 Median and ulnar nerve in the forearm and hand