Radial & Ulnar Nerves Anatomy Quiz

Radial & Ulnar Nerves

• Objectives: Students should be able to describe the anatomy of the radial and ulnar nerves, including origin, course, and distribution. They should also list the branches of these nerves and describe causes and manifestations of nerve injuries.

Radial Nerve

• Origin: Posterior cord of the brachial plexus in the axilla, the largest branch.
• Supply: All muscles of the posterior compartment of the arm and forearm.
• Course & Distribution: Winds around the back of the arm in the spiral groove on the humerus, between the heads of the triceps. It's accompanied by the profunda vessels and lies directly in contact with the humerus shaft.
• Branches (in the Axilla): Cutaneous – posterior cutaneous nerve of arm. Muscular – long and medial heads of triceps.
• Branches (in the Spiral Groove): Cutaneous – lower lateral cutaneous nerve of arm, posterior cutaneous nerve of forearm. Muscular – lateral and medial heads of triceps, anconeus
• Branches (in the Arm): Pierces the lateral intermuscular septum, descends in front of the lateral epicondyle, passes forward into the cubital fossa and divides into superficial and deep branches.
• Branches (close to lateral epicondyle): Muscular – brachioradialis, extensor carpi radialis longus, and brachialis. Articular – to the elbow joint
• Superficial Branches: Descends under the cover of brachioradialis, lateral to the radial artery, and emerges beneath the brachioradialis tendon.
• Termination of Superficial Branch: Reaches the posterior surface of the wrist, dividing into terminal branches supplying skin. Supplies the lateral two-thirds of the posterior surface of the hand and the proximal phalanges of the lateral three-and-a-half fingers. The area of skin supplied varies.
• Deep Branch: Winds around the neck of the radius, inside the supinator muscle, and enters the posterior compartment of the forearm. It supplies: Extensor carpi radialis brevis, Supinator, Abductor pollicis longus, Extensor pollicis brevis, Extensor pollicis longus, Extensor indicis.

Injuries of the Radial Nerve

• In the Axilla: Injury can occur due to drunkard falling asleep with one arm over the back of a chair, or due to fractures/dislocations of the proximal humerus. Effects include paralysis of the triceps, anconeus, and long extensors, resulting in inability to extend the elbow, wrist, and fingers(wrist drop).
• In the Spiral Groove: Injury or fracture of the spiral groove of the humerus leads to inability to extend the wrist and fingers (wrist drop).
• Injuries to the Deep Branch: The deep branch is purely motor, supplying the extensor muscles. Damage typically occurs in fractures of the proximal radius or during dislocation of the radial head. The resultant impairment is limited to motor function. Sensory function is not affected.

Ulnar Nerve

• Origin: Medial cord of brachial plexus.
• Course: Descends along the medial side of the following arteries – axillary, brachial. Pierces medial intermuscular septum, passing behind the medial epicondyle of the humerus.
• In the Forearm: Enters the anterior compartment; descends behind the flexor carpi ulnaris; medial to the ulnar artery.
• At the Wrist: Passes anteriorly to the flexor retinaculum; later to the pisiform bone; and medial to the ulnar artery; divides into superficial and deep branches.
• Branches (in the Forearm): Muscular (to flexor carpi ulnaris, and medial half of flexor digitorum profundus), and articular (to the elbow joint).
• Branches (at the Wrist): Cutaneous (dorsal and palmar); Muscular (to palmaris brevis); Cutaneous (to skin on the medial part of the palm) and deep terminal branch (to the hypothenar eminence, interossei, third and fourth lumbricals and adductor pollicis), and articular (to carpal joints).

Ulnar Nerve Injury

• At the Elbow: Atrophy of the ulnar side of forearm, flexion of wrist with abduction, claw hand, wasting of hypothenar eminence.
• At the Wrist: Claw hand, wasting of hypothenar eminence.

Cutaneous Nerves of Hand

• Autonomous areas for testing: Ulnar, Median, Radial. -Ulnar: digital branches, palmar cutaneous branch ,dorsal cutaneous branch -Median: digital branches, palmar cutaneous branch -Radial: dorsal cutaneous branch

References

• Gray's Anatomy for Students, Fourth edition
• Snell Clinical Anatomy, Ninth edition
• Clinically Oriented Anatomy, Keith L. Moore – Seventh edition
• Netter's Clinical Anatomy, Second edition