Upper Extremity Nerves

General Rules

Key recommendations include careful marking of stimulation and recording points, precise distance measurement following nerve anatomy, and understanding amplitude changes between distal and proximal stimulation.

Temperature Considerations

At lower skin temperatures, sensory and motor amplitudes become higher and distal latencies are prolonged. Optimal temperature is 35°C.

The Median Nerve

The median nerve arises from the lateral and medial cords of the brachial plexus (C6-T1). It provides motor innervation to forearm flexors and thenar muscles, and sensory innervation to the palmar aspect of the thumb, index, middle, and radial half of the ring finger.

Common entrapment sites include:

• Carpal tunnel (most common)
• Pronator teres muscle
• Ligament of Struthers

The Ulnar Nerve

The ulnar nerve arises from the medial cord (C8-T1). It provides motor innervation to hand intrinsics and sensory innervation to the little finger and ulnar half of the ring finger.

Common entrapment sites include:

• Cubital tunnel at the elbow (most common)
• Guyon’s canal at the wrist

The Radial Nerve

The radial nerve arises from the posterior cord (C5-T1). It provides motor innervation to arm and forearm extensors and sensory innervation to the posterior arm, forearm, and dorsal hand.

Common entrapment sites include:

• Spiral groove of the humerus
• Posterior interosseous nerve in the forearm

The Musculocutaneous, Axillary, and Spinal Accessory Nerves

Musculocutaneous nerve: Innervates biceps and brachialis; becomes the lateral antebrachial cutaneous nerve providing sensory to lateral forearm.

Axillary nerve: Innervates deltoid and teres minor; provides sensory to lateral shoulder.

Spinal accessory nerve: Motor nerve to trapezius and sternocleidomastoid muscles.