Anatomy: Nerves - Arm / Forearm / Hand

Nerves - Arm / Forearm / Hand

Musculocutaneous nerve  Pierces the coracobrachialis muscle and descends between the biceps and brachialis muscles. Innervates all of the flexor muscles in the anterior compartment of the arm, such as the coracobrachialis, biceps, and brachialis muscles. Continues into the forearm as the lateral antebrachial cutaneous nerve. Median nerve  Runs down the anteromedial aspect of the arm, and at the elbow, it lies medial to the brachial artery on the brachialis muscle (has no muscular branches in the arm). Passes through the cubital fossa, deep to the bicipital aponeurosis and medial to the brachial artery. Enters the forearm between the humeral and ulnar heads of the pronator teres muscle, passes between the flexor digitorum superficialis and the flexor digitorum profundus muscles, and then becomes superficial by passing between the tendons of the flexor digitorum superficialis and flexor carpi radialis near the wrist. In the cubital fossa, gives rise to the anterior interosseous nerve , which descends on the interosseous membrane between the flexor digitorum profundus and the flexor pollicis longus; passes behind the pronator quadratus, supplying these three muscles; and then ends in sensory “twigs― to the wrist joint. Innervates all of the anterior muscles of the forearm except the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus. Enters the palm of the hand through the carpal tunnel deep to the flexor retinaculum; gives off a muscular branch (recurrent branch ) to the thenar muscles; and terminates by dividing into three common palmar digital nerves , which then divide into the palmar digital branches. Innervates also the lateral two lumbricals, the skin of the lateral side of the palm, and the palmar side of the lateral three and one-half fingers and the dorsal side of the index finger,middle finger, and one half of the ring finger. Radial nerve  Arises from the posterior cord and the largest branch of the brachial plexus. Descends posteriorly between the long and medial heads of the triceps, after which it passes inferolaterally with the profunda brachii artery in the spiral (radial) groove on the back of the humerus between the medial and lateral heads of the triceps. Pierces the lateral intermuscular septum to enter the anterior compartment and descends anterior to the lateral epicondyle between the brachialis and brachioradialis muscles to enter the cubital fossa, where it divides into superficial and deepbranches. Gives rise to muscular branches (which supply the brachioradialis and extensor carpi radialis longus), articular branches, and posterior brachial and posterior antebrachial cutaneous branches. 1. Deep branch Enters the supinator muscle, winds laterally around the radius in the substance of the muscle,and supplies the extensor carpi radialis brevis and supinator muscles. Continues as the posterior interosseous nerve with the posterior interosseous artery and innervates the rest of the extensor muscles of the forearm. 2. Superficial branch Descends in the forearm under cover of the brachioradialis muscle and then passes dorsally around the radius under the tendon of the brachioradialis. Runs distally to the dorsum of the hand to innervate the skin of the radial side of the hand and the radial two and one-half digits over the proximal phalanx. This nerve does not supply the skin of the distal phalanges. Ulnar nerve Arises from the medial cord of the brachial plexus, runs down the medial aspect of the arm, pierces the medial intermuscular septum at the middle of the arm, and descends together with the superior ulnar collateral branch of the brachial artery. Descends behind the medial epicondyle in a groove or tunnel (cubital tunnel), where it is readily palpated and most commonly injured. It may be damaged by a fracture of the medial epicondyle and produce funny bone symptoms. Enters the forearm by passing between the two heads of the flexor carpi ulnaris and descends between and innervates the flexor carpi ulnaris and flexor digitorum profundus muscles. Enters the hand superficial to the flexor retinaculum and lateral to the pisiform bone, where it is vulnerable to damage from cuts or stab wounds. Terminates by dividing into superficial and deep branches at the root of the hypothenar eminence. 1. Superficial branch Innervates the palmaris brevis and the skin over the palmar and dorsal surfaces of the medial one third of the hand, including the hypothenar eminence. Terminates in the palm by dividing into three palmar digital branches , which supply the skin of the little finger and the medial side of the ring finger. 2. Deep branch Arises at and travels through the Guyon's canal, and then passes between the pisiform and the hook of the hamate, and then deep to the opponens digiti minimi. Curves medial to the hook of the hamate, and then turns laterally to follow the course of the deep palmar arterial arch across the interossei, and then runs between two heads of the adductor pollicis. Innervates the hypothenar muscles, the medial two lumbricals, all of the interossei, the adductor pollicis, and usually the deep head of the flexor pollicis brevis.

Nerves of the Arm, Forearm, and Hand

Functional Components of the Peripheral Nerves

Somatic motor nerves Include radial, axillary, median, musculocutaneous, and ulnar nerves and ventral or dorsal primary rami and other nerves. Contain nerve fibers with cell bodies that are located in the following structures: Dorsal root ganglia for general somatic afferent (GSA) and general visceral afferent (GVA) fibers. Anterior horn of the spinal cord for general somatic efferent (GSE) fibers. Sympathetic chain ganglia for sympathetic postganglionic general visceral efferent fibers (GVE). Cutaneous nerves Include medial brachial, medial antebrachial, lateral antebrachial, and other cutaneous nerves. Contain nerve fibers with cell bodies that are located in the following structures: Dorsal root ganglia for GSA and GVA fibers. Sympathetic chain ganglia for sympathetic postganglionic GVE fibers.