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Median Nerve

Contents

Introduction

The upper limb is one of the reasons our species has evolved to be so dominant. It enables us to grip, throw and strike. In order to understand the significance of the upper limb, we cannot ignore the median nerve. It gives us one of the most essential functions of life, opposing our thumb which is important to do precision handling and perform lots of activities like writing, threading a needle or winding a watch. In this article we will discuss the anatomy of the median nerve as well as the clinical points related to it.

Recommended video: Median nerve
Distribution and anatomy of the median nerve.

Innervation

The median nerve is a major peripheral nerve and supplies the flexor muscles in the forearm except flexor carpi ulnaris and the ulnar head of flexor digitorum profundus, which is supplied by the ulnar nerve. It also supplies the muscles of the thenar eminence as well as the radial two lumbricals.

Median nerve - ventral view

Median nerve - ventral view

Origin & Nerve Roots

The nerve roots of the median nerve are from the ventral rami of the C6-T1 nerves. The median nerve is formed by the unification of the medial and lateral cords. It can be seen as the central line of an ‘M Shaped’ brachial plexus, the cords of which surround the axillary artery.

Median nerve - ventral view

Median nerve - ventral view

Course

Arm

After its formation from the medial and lateral cords of the brachial plexus, the median nerve descends down the centre of the arm in a superficial course. Initially it is lateral to the brachial artery but as it descends it eventually becomes medial. It gives no branches in the arm.

Median nerve - ventral view

Median nerve - ventral view

Forearm

Just before it enters the forearm, the median nerve passes between the tendons of biceps brachii and brachialis. At this point it becomes lateral to the brachial artery. Next, in order to gain access to the forearm, it passes between the deep and superficial heads of the pronator teres muscle. Once it passes this point it dives deeper and runs between the flexor digitorum profundus and superficialis. It gives: 

  • muscular branches to pronator teres, palmaris longus, flexor digitorum superficialis and flexor carpi radialis
  • the anterior interosseus nerve
  • the cutaneous nerve of the palm

The anterior interosseous nerve supplies the flexor pollicis longus and radial part of flexor digitorum profundus. This branch runs on the interosseous membrane with anterior interosseous artery passes deep to the pronator quadratus and supplies it. It terminates by giving articular branches to the distal radio ulnar, radiocarpal and carpal joints. It also supplies to the proximal part of the palm, via the palmar cutaneous branch. This branch does not enter the carpal tunnel and is hence spared in carpal tunnel syndrome.

Anterior interosseous artery and nerve - ventral view

Anterior interosseous artery and nerve - ventral view

Hand

Median nerve passes through the carpal tunnel beneath the flexor retinaculum, and divides to form two common palmar digital nerves, the first of which supplies the radial two lumbricals and a common branch between the index and middle fingers. The second runs between the ring and middle finger, and divides to give the proper digital nerves. The branch also provides sensation to the radial three and a half fingers on their palmar aspect as well as the nail beds of the index, middle and half the ring finger, via the proper digital nerves.

Proper palmar digital nerves of the median nerve - ventral view

Proper palmar digital nerves of the median nerve - ventral view

The median nerve also gives off a recurrent branch to the muscles of the thenar eminence (flexor pollicis brevis, abductor pollicis brevis, opponens pollicis). It is also known as the ‘million dollar nerve’ to signify its importance for basic hand function. The reason it is referred to as the recurrent branch is due to the course it takes. It wraps around the flexor pollicis brevis and then arches back to pass into the thenar eminence. This does not include adductor pollicis, which although moves the thumb is not a part of the thenar eminence and is supplied by a deep branch of the ulnar nerve.

Clinical Notes

Carpal Tunnel Syndrome

The median nerve passes within the carpal tunnel and runs deep to the flexor retinaculum. If the tendons of the long finger flexors become swollen due to overuse (typist), or oedema (pregnancy), then the median nerve becomes compressed. This results in pain, paresthesia and numbness (tingling and pins and needles) of the lateral three and a half fingers. Tapping over the median nerve in the carpal tunnel (‘Tinel’s maneuver’) results in numbness or pain in the median nerve distribution. Flexion of the wrist for 60 seconds will also elicit pain or numbness. Symptoms include thenar muscle wasting and weakness. Treatment is with surgical compression.

Hand of Benediction

The median nerve is vulnerable to be damaged at the elbow, commonly from a supracondylar fracture. This results in the radial head of flexor digitorum profunda being denervated. The forearm is constantly supinated and the lateral two lumbricals have also been denervated, the flexion at the metacarpophalangeal and interphalangeal joints of 2 & 3 digits is lost. There is inability to make a fist as both of these fingers are extended and the hand is in a classic position known as the ‘hand of benediction’ (when the person tries to flex their fingers).

Simian/Ape Hand Deformity

If the recurrent motor branch of the median nerve is damaged, the muscles of the thenar eminence become denervated. This includes abductor pollicis brevis, flexor pollicis brevis, opponens pollicis and the two radial lumbricals. This results in the person becomes unable to oppose the thumb i.e. bring the tip of the thumb to the tip of the other fingers. The appearance is that of an ape’s hand, due to the unopposable thumb. This is distinguished from the hand of benediction as the radial head of flexor digitorum profundus is still functional.

Pronator syndrome

The median nerve can become trapped between the two heads of pronator teres, resulting in wrist flexor wasting.

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Show references

References:

  • Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head and Neck.
  • Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
  • Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.

Author, Review and Layout:

  • Shahab Shahid
  • Uruj Zehra
  • Catarina Chaves

Illustrators:

  • Median nerve - ventral view - Begoña Rodriguez
  • Median nerve - ventral view - Begoña Rodriguez
  • Median nerve - ventral view - Yousun Koh
  • Anterior interosseous artery and nerve - ventral view - Yousun Koh
  • Proper palmar digital nerves of the median nerve - ventral view - Yousun Koh
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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