Upper Limb Nerves Anatomy

The median nerve enters the arm at the inferior margin of the teres major muscle, traveling along the medial side of the arm in the anterior compartment, closely associated with the brachial artery.

The median nerve lies lateral to the brachial artery in the proximal region of the arm, but crosses to its medial side and lies anterior to the elbow joint in more distal regions.

The ulnar nerve enters the arm with the median nerve and axillary artery, initially medial to the axillary artery. It then penetrates the medial intermuscular septum, entering the posterior compartment and traveling behind the medial epicondyle of the humerus before re-entering the anterior compartment of the forearm.

The radial nerve originates from the posterior cord of the brachial plexus and enters the arm, positioned behind the brachial artery. It then passes through the triangular interval, reaching the posterior compartment of the arm.

The radial nerve lies in the radial groove, directly on bone, as it travels diagonally through the posterior compartment. It then passes through the lateral intermuscular septum to the anterior compartment, situated between the brachialis and brachioradialis muscles.

The radial nerve innervates several muscles in the arm, including the triceps brachii, brachioradialis, extensor carpi radialis longus, and partially the brachialis muscle.

The radial nerve gives rise to cutaneous branches, including the inferior lateral cutaneous nerve of the arm and the posterior cutaneous nerve of the forearm, which become subcutaneous.

The radial nerve is responsible for the extension of the arm and forearm, while the median nerve controls flexion and pronation, and the ulnar nerve contributes to flexion and also innervates muscles for hand movements.