The brachial plexus nerve has so many branches

The brachial plexus is an important part of the human nervous system and is related to the normal functioning of human nerve functions, so it is necessary for people to have a certain understanding of it. The brachial plexus has seven main branches: the musculocutaneous nerve, median nerve, ulnar nerve, radial nerve, axillary nerve, long thoracic nerve, and thoracodorsal nerve. Each nerve plays a different role and is interconnected.

1. Introduction

The brachial plexus is composed of the anterior rami of the 5th to 8th cervical nerves and most of the anterior rami of the first thoracic nerve. It passes through the gap between the scalene muscles, runs above and behind the subclavian artery, and enters the axilla through the back of the clavicle. The fibers of the five roots of the brachial plexus are first combined into the upper, middle and lower trunks, which then send branches around the axillary artery to form the medial, lateral and posterior bundles. The branches sent out from the bundles are mainly distributed in the upper limbs and some superficial muscles of the chest and back.

2. Main branches

The branches of the brachial plexus are concentrated and superficial behind the midpoint of the clavicle, and brachial plexus block anesthesia is often performed here in clinical practice. The main branches of the brachial plexus are:

1. Musculocutaneous nerve

It branches out from the lateral bundle and goes obliquely outward and downward through the coracobrachialis muscle, then goes down between the biceps brachii and brachialis muscle, and sends out branches to innervate these three muscles. The terminal branch is on the outside slightly above the elbow joint, penetrates the deep fascia to the subcutaneous tissue, and is renamed the lateral antebrachial cutaneous nerve, which is distributed in the skin on the outside of the forearm.

2. Median nerve

Two of them originate from the inner and outer bundles respectively, and clamp the axillary artery. It converges into the median nerve at an acute angle downward, and then descends along the medial edge of the biceps along with the brachial artery to the antecubital fossa, passes through the pronator teres muscle, and descends between the superficial and deep flexor muscles of the forearm, through the carpal tunnel to the palm. First, the median nerve sends out its reverse branch and enters the thenar eminence, followed by the three palmar digital nerves, which then divide into two palmar proper nerves to the relative edges of the 1st to 4th fingers.

The median nerve has no branches in the arm, but it gives off muscle branches at the elbow, forearm, and palm, innervating all forearm muscles except the brachioradialis, ulnar flexor carpi, and ulnar half of the flexor digitorum profundus. In the palm, it innervates the thenar muscles and the first and second lumbrical muscles except the adductor pollicis. Its cutaneous branches control the sensation of the radial 2/3 of the palm, the palmar surface of the radial three and a half fingers, and the middle and distal segments of the skin on the back.

Median nerve injury often occurs in the forearm and wrist. The main symptoms after injury are: ① movement disorder, manifested as inability to pronate the forearm, weakened wrist flexion, inability to flex the thumb, index finger and middle finger, and inability of the thumb to do palm-to-palm movement; ② sensory disorder, manifested as sensory disorder in the distribution area of ​​the cutaneous branches, especially in the distal segments of the thumb, index finger and middle finger; ③ hand deformity. The thenar muscles atrophy, the palm becomes flat, and "ape hands" are formed.

3. Ulnar nerve

It originates from the medial bundle of the brachial plexus, emerges from the axilla between the axillary artery and vein, descends along the medial edge of the biceps along with the brachial artery, passes through the medial intermuscular septum to the back of the arm in the middle of the arm, and then descends through the ulnar nerve groove behind the medial epicondyle. At this point, its position is superficial. The ulnar nerve runs along the deep surface of the ulnar flexor carpi ulnaris of the forearm along with the ulnar artery, and gives off the dorsal branch of the ulnar nerve above the radiocarpal joint. This trunk then runs down through the radial side of the pisiform bone and is divided into the superficial branch and the deep branch into the palm.

The ulnar nerve sends out muscular branches in the forearm to innervate the ulnar flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus; in the palm of the hand, it sends out deep branches to innervate the hypothenar muscles, adductor pollicis, interosseous muscles, and the 3rd and 4th lumbrical muscles. The cutaneous branches of the ulnar nerve are distributed in the skin of the hypothenar eminence and one and a half fingers on the ulnar side on the palm; and in the skin of the ulnar 1/2 of the dorsum, one and a half fingers on the ulnar side, the radial half of the proximal segment of the ring finger, and the ulnar half of the proximal segment of the middle finger on the dorsum of the hand.

Supracondylar fractures of the humerus are prone to injury to the ulnar nerve. The main symptoms after damage to the ulnar nerve are weak wrist flexion, inability to flex the distal segments of the ring finger and little finger; the hypothenar muscle atrophies and becomes flat, and the thumb cannot be adducted; the interosseous muscles atrophy, deep grooves appear between the metacarpal bones, and the fingers cannot come close to each other; the metacarpophalangeal joints are overturned, and the interphalangeal joints of the 4th and 5th fingers are bent, forming a "claw hand". Loss of sensation on the inner edge of the palm and back of the hand.

4. Radial nerve

It is a thick nerve that originates from the posterior bundle. It is initially behind the axillary artery, then goes posteriorly along with the deep brachial artery, and then goes downward and outward close to the radial nerve groove on the deep surface of the triceps brachii. It is divided into superficial and deep branches in front of the lateral epicondyle of the humerus. The superficial branch of the radial nerve runs along the deep surface of the brachioradialis muscle along with the radial artery, turns to the dorsum of the hand at the junction of the middle and lower 1/3 of the forearm, and is distributed in the skin on the back of the radial 1/2 of the dorsum of the hand and the proximal segments of the radial 2.5 fingers. The deep branch of the radial nerve descends between the deep and superficial muscles on the back of the forearm and is divided into several branches, with the long branch reaching the wrist.

The muscular branches of the radial nerve innervate the triceps brachii, brachioradialis, and all the posterior forearm muscles. In addition to the above, cutaneous branches are also distributed in the skin on the back of the arms and forearms.

Humeral shaft fractures are prone to damage the radial nerve. The motor impairment after injury is mainly manifested as paralysis of the forearm extensor muscles, inability to extend the wrist and fingers, and a "drop wrist sign" when raising the forearm; the sensory impairment is most obvious in the skin of the "tiger's mouth area" on the back of the 1st and 2nd metacarpal gap.

5. Axillary nerve

It arises from the posterior bundle of the brachial plexus, and travels with the posterior humeral circumflex artery around the back of the surgical neck of the humerus to the deep surface of the deltoid muscle.

The fascicular branches innervate the deltoid and teres minor muscles.

The cutaneous branches pass through the posterior edge of the deltoid muscle and are distributed in the skin of the lateral surface of the upper 1/3 of the shoulder and arm.

Fracture of the surgical neck of the humerus, dislocation of the shoulder or compression of the axillary crutch can all cause damage to the axillary nerve. The main manifestations after injury are paralysis of the deltoid muscle, reduced or inability to abduct the shoulder joint, and sensory impairment of the skin in the deltoid area. If the deltoid muscle atrophies, the shoulder loses its round appearance, the acromion protrudes, and a "square shoulder" deformity is formed.

6. Long thoracic nerve

It arises from the brachial plexus above the clavicle, descends along the lateral surface of the serratus anterior muscle, and innervates this muscle. Damage to this nerve can cause paralysis of the serratus anterior muscle, manifesting as "winged scapula", difficulty raising the upper limbs, and inability to comb the hair.

7. Thoracodorsal nerve

It originates from the posterior bundle, descends along the lateral edge of the scapula along with the subscapular vessels, and is distributed in the latissimus dorsi muscle. When removing lymph nodes during radical mastectomy, be careful not to damage this nerve. You cannot do back-hand movements after the injury.