Human Anatomy - Kotsan I. Ya. 2009

Peripheral Nervous System
Spinal Nerves
Long Branches of the Brachial Plexus

The Long branches of the Brachial Plexus originate from the infraclavicular part of the brachial plexus, specifically from its lateral, medial, and posterior cords. These branches include the median nerve, ulnar nerve, medial cutaneous nerve of the arm, medial cutaneous nerve of the forearm, musculocutaneous nerve, and radial nerve.

The median nerve (n. medianus) arises from two roots—a medial ROOT (radix medialis (C_VIII-Th_I)) and a lateral root (radix lateralis (C_VI-C_VII))—from the medial and lateral cords of the brachial plexus, respectively. The roots unite to form a single trunk anterior to the axillary artery; the nerve then descends in the arm within the medial bicipital groove alongside the brachial artery and Veins. Throughout its course in the arm, the median nerve gives off no branches. In the cubital fossa, the nerve passes beneath the aponeurosis of the biceps brachii, pierces the pronator teres Muscle, and enters the median groove on the forearm. Passing through the carpal tunnel, the median nerve enters the hand and divides into the common palmar digital nerves.

In the forearm, the median nerve gives off muscular branches (rr. musculares) that innervate almost all Muscles of the anterior compartment of the forearm, except for the flexor carpi ulnaris and the medial part of the flexor digitorum profundus. The largest branch of the median nerve in the forearm is the anterior interosseous nerve of the forearm (n. interosseus antebrachii anterior), which descends along the anterior surface of the interosseous membrane together with the anterior interosseous artery. This branch innervates the Deep Muscles of the anterior forearm and sends a branch to the anterior portion of the wrist joint.

In the hand, the median nerve innervates the abductor pollicis brevis, the opponens pollicis, the superficial HEAD of the flexor pollicis brevis, and the first to third lumbrical muscles. Even before entering the carpal tunnel, the median nerve gives off a small palmar branch of the median nerve (r. palmaris n. mediani), which innervates the Skin over the anterior aspect of the wrist joint and the thenar eminence in the middle of the palm.

The terminal Branches of the median nerve are three common palmar digital nerves (nn. digitales palmares communes), which run along the first, second, and third intermetacarpal spaces beneath the superficial palmar arterial arch and the palmar aponeurosis. The first common palmar digital nerve innervates the first lumbrical muscle and gives off three cutaneous branches—the proper palmar digital nerves (nn. digitales palmares proprii). Two of these run along the radial and ulnar sides of the thumb, and the third runs along the radial side of the index finger, providing sensory innervation to the skin of these areas. The second and third common palmar digital nerves give off two proper palmar digital nerves each, which supply the skin of the opposing surfaces of the second, third, and fourth digits, as well as the skin of the dorsal aspect of the distal Phalanges of the second and third digits. In addition, the second lumbrical muscle is innervated by the second common palmar digital nerve.

The ulnar nerve (n. ulnaris) originates from the medial cord of the brachial plexus (C_VII, VIII-ThI), passes down the medial side of the arm to the posterior aspect of the medial epicondyle (where it lies superficially just beneath the skin, making it prone to impact that causes a tingling sensation in the medial forearm), and then enters the ulnar groove. Here it runs alongside the corresponding artery and veins, distally continuing as its terminal palmar branch (r. palmaris n. ulnaris). In the arm, much like the median nerve, the ulnar nerve gives off no branches.

In the forearm, the ulnar nerve gives off muscular branches (rr. musculares) that innervate the flexor carpi ulnaris and the ulnar part of the flexor digitorum profundus, as well as a small articular branch that supplies the capsule of the elbow joint. In the lower third of the forearm, the dorsal branch of the ulnar nerve (r. dorsalis n. ulnaris) arises, passes to the dorsal aspect of the hand, and through its terminal branches—the dorsal digital nerves (nn. digitales dorsales)—innervates the skin of the little finger, the ring finger, and the ulnar side of the middle finger.

The palmar branch of the ulnar nerve (r. palmaris n. ulnaris) is the continuation of the ulnar nerve proper. At the level of the pisiform bone, this branch divides into superficial and deep branches. The superficial branch (r. superficialis) runs superficially beneath the skin, gives off a muscular branch to the palmaris brevis muscle, and continues as the common palmar digital nerve (n. digitalis palmaris communis), which runs in the fourth interosseously space and divides into two proper palmar digital nerves (nn. digitales palmares proprii). These supply the skin of the adjacent sides of the fourth and fifth digits on the palmar aspect, as well as the skin of the middle and distal phalanges of these digits on the dorsal aspect. The deep branch (r. profundus) travels with the deep branch of the ulnar artery, accompanies the deep palmar arterial arch, and gives off branches that innervate the abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi, interossei muscles, third and fourth lumbricals, adductor pollicis, and the deep head of the flexor pollicis brevis.

The medial cutaneous nerve of the arm (n. cutaneus brachii medialis) (C_VIII-Th_I) arises from the medial cord of the brachial plexus, accompanies the brachial artery, typically communicates with the perforating branch of the second thoracic nerve (the intercostobrachial nerve), and innervates the skin on the Medial surface of the arm down to the elbow joint.

The medial cutaneous nerve of the forearm (n. cutaneus antebrachii medialis) (C_VIII-Th_I) also originates from the medial cord of the brachial plexus. In the axilla, it lies adjacent to the ulnar nerve; in the upper arm, it is situated medial to the brachial artery alongside the basilic vein of the upper limb, piercing the fascia together with it to become subcutaneous. This nerve innervates the skin on the ulnar (medial) side of the forearm down to the wrist joint.

The musculocutaneous nerve (n. musculocutaneus) (C_V-C_VII) branches off from the lateral cord of the brachial plexus, pierces the coracobrachialis muscle, and descends between the biceps brachii and brachialis muscles. In the cubital fossa, the nerve runs in the anterior lateral cubital groove and continues into the forearm as the lateral cutaneous nerve of the forearm. In the arm, the musculocutaneous nerve gives off muscular branches (rr. musculares) that innervate the coracobrachialis, brachialis, and biceps brachii muscles. In the forearm, the lateral cutaneous nerve of the forearm (n. cutaneus antebrachii lateralis) innervates the skin of the anterolateral surface of the forearm.

The radial nerve (n. radialis) (C_V-Th_I) is the continuation of the posterior cord of the brachial plexus. In the axilla, the radial nerve is located posterior to the axillary artery and lies deeper than the aforementioned nerves; it runs downward, laterally, and posteriorly, winds around the humerus dorsally, and upon reaching the lateral epicondyle of the humerus, divides into deep and superficial branches. Along its course, the radial nerve gives off the following branches:

The muscular branches (rr. musculares) of the radial nerve innervate all posterior muscles of the arm—the triceps brachii and anconeus—as well as select lateral muscles of the forearm (the brachioradialis and extensor carpi radialis longus).

The posterior cutaneous nerve of the arm (n. cutaneus brachii posterior) branches off from the radial nerve within the axillary cavity, ramifies in the skin of the posterior surface of the arm, and provides its innervation.

The inferior lateral cutaneous nerve of the arm (n. cutaneus brachii lateralis inferior) arises from the radial nerve in the arm and innervates the skin of the lateral surface of the arm inferior to the deltoid region.

The posterior cutaneous nerve of the forearm (n. cutaneus antebrachii posterior) originates from the radial nerve in the arm and distributes branches to the skin of the posterior forearm.

The superficial branch (r. superficialis) of the radial nerve descends in the forearm within the radial groove alongside the radial artery and veins. Slightly proximal to the wrist joint, the nerve pierces the forearm fascia and passes onto the dorsum of the hand, where it divides into 5 dorsal digital nerves (nn. digitales dorsales) that innervate the skin of the dorsal surfaces of the proximal phalanges of the first two digits on both sides and of the middle digit on the lateral side.

The deep branch (r. profundus) of the radial nerve passes through the supinator muscle of the forearm, supplying it with a small branch, then winds laterally around the neck of the radius. Emerging onto the posterior surface of the forearm, it innervates all muscles located in the posterior compartment. Its terminal and longest branch is the posterior interosseous nerve of the forearm (n. interosseus antebrachii posterior), which runs along the posterior surface of the interosseous membrane to the hand, sending fine branches to the interosseous membrane, forearm bones, and the intercarpal, carpometacarpal, and metacarpophalangeal JOINTS OF THE hand.

Data regarding the NERVES OF THE brachial plexus are presented in Table 10.

Class="center">Table 10 NERVES OF THE BRACHIAL PLEXUS