Albany Medical College Virtual Anatomy Lab

Lab3 - Module 1 - Anatomy of the Arm: Page 9 of 9

Nerves of the Arm

Brachial Plexus
Brachial Plexus
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The four nerves of the arm (Median, Ulnar, Musculocutaneous, and Radial) are terminal branches of the Brachial Plexus.
Remove the Deltoid and Veins of the arm.
The nutrient humeral artery, and the superior and inferior ulnar collateral arteries are not visable in the 3D cadaver.
Observe the Median Nerve. This major nerve is formed in the axilla by the union of a lateral root from the lateral cord and a medial root from the medial cord of the brachial plexus. The nerve runs on the lateral side of the brachial artery until it reaches the middle of the arm, where it crosses to its medial side and contacts the brachialis muscle. The median nerve descends into the cubital fossa. This nerve has no branches in the axilla or in the arm except when the musculocutaneous nerve doesn’t exist. In that case the median nerve will send muscular branches to the muscles of the anterior arm.
• Injury to the median nerve proximal to the elbow results in loss of sensation on the lateral portion of the palm, the palmar surface of the thumb, flexion of the wrist and fingers, and important movements of the thumb are lost or severely affected.
Observe the Ulnar Nerve. The larger of the two terminal branches of the medial cord of the brachial plexus. It passes anterior to the triceps on the medial side of the brachial artery; at the middle of the arm it pierces the medial intermuscular septum and descends between it and the medial head of the triceps muscle. The ulnar nerve enters the forearm by passing between the medial epicondyle of the humerus and the olecranon process of the ulna. Posterior to the medial epicondyle of the humerus, the ulnar nerve is superficial and easily palpable (hitting the ulnar nerve here has resulted in the term “funny bone” – ha-ha). The ulnar nerve has no branches in the arm, but supplies one and one-half muscles in the forearm.
• Injury to the ulnar nerve in the arm results in impaired flexion and adduction of the wrist and impaired movement of the thumb, ring, and little fingers. Characteristic clinical sign of ulnar nerve damage is inability to adduct or abduct the medial four digits.
Remove the Biceps Brachii muscle and add the Musculocutaneous Nerve. This nerve is one of the terminal branches of the lateral cord of the brachial plexus. It pierces the coracobrachialis muscle and then continues between the biceps brachii and brachialis muscles, supplying all three of them. At the lateral border of the distal biceps tendon it becomes the lateral antebrachial cutaneous nerve (AKA lateral cutaneous nerve of the forearm). Not visualized on this 3D Cadaver.
• Injury to the musculocutaneous nerve in the axilla results in flexion of the elbow joint and supination of the forearm being greatly weakened.
Add the Radial Nerve. This nerve is one of the terminal branches of the posterior cord of the brachial plexus. It enters the arm posterior to the brachial artery, medial to the humerus, and anterior to the long head of the triceps brachii muscle. The radial nerve passes inferolaterally with the profunda (deep) brachii artery around the body of the humerus in the radial (spiral) groove. At the lateral border of the numerus, the nerve pierces the lateral intermuscular septum and continues between the brachialis and brachioradialis muscles to the lateral epicondyle of the humerus, where it divides into the deep and superficial branches. After the deep branch of the radial nerve emerges from the supinator muscle, it is called the posterior (dorsal) interosseous nerve. The deep branch of the radial nerve is entirely muscular and articular in its distribution, while the superficial branch supplies sensory fibers to the dorsum of the hand and fingers.
• Injury to the radial nerve proximal to the origin of the triceps results in paralysis of the triceps brachii, brachioradialis, supinator, and extensors of the wrist, thumb, and fingers, as well as loss of sensation to the skin supplied. Characteristic clinical sign of radial nerve injury is wrist drop, i.e., inability to extend or straighten the wrist.

Based on what you have just learned, are you suspicious of any of these structures being involved with the above case report? If so, what structures and why?