Median Nerve

Median Nerve

Question. Describe the median nerve under the following headings: (a) root value, (b) course and relations, (c) branches and distribution, and (d) applied anatomy.
Answer.

The median nerve is so called because it runs in the median plane of the forearm.

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Median Nerve Root value

Ventral rami of C5 to C8 and T1.

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Median Nerve Course and Relations

The median nerve is formed in the axilla by two roots – the lateral root from the lateral cord of the brachial plexus and the medial root from the medial cord of the brachial plexus. Then it courses successively through four regions: axilla, arm, forearm, and palm. The medial root crosses the axillary artery to join the lateral root.

Axilla:

In the axilla, the median nerve lies first anterior and then lateral to the axillary artery.

Arm:

In the arm, the median nerve continues to run on the lateral side of brachial artery till the midarm (i.e. insertion of coracobrachialis), where it crosses in front of the brachial artery to lie on its medial side, and then passes anterior to elbow joint to enter the forearm.

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Forearm:

In the forearm, the median nerve passes through the cubital fossa, lying medial to the brachial artery. It leaves the fossa between the two heads of pronator teres before crossing superficial to the ulnar artery from medial to lateral side and giving its anterior interosseous branch below this.

Then it passes deep to the fibrous arch of the flexor digitorum superficialis. It adheres to the deep surface of the flexor digitorum superficialis and leaves the muscle long its lateral border. About 5 cm above the wrist, it lies between the tendons of palmaris longus and flexor carpi radialis. It enters the palm through the carpal tunnel under the flexor retinaculum, but in front of the common synovial sheath enclosing tendons of the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP).

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Palm:

In the palm at the distal border of the flexor retinaculum, it ends by dividing into lateral and medial terminal branches. Before dividing into terminal branches, the median nerve gives off a recurrent muscular branch from its lateral side.

Median Nerve Branches and Distribution

In the axilla:

No branch

In arm:

Muscular branch to pronator teres

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In the cubital fossa

• Muscular branches to:
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor digitorum superficialis

In the forearm

• Anterior interosseous nerve, which supplies:
  • Lateral half of FDP
  • Flexor pollicis longus
  • Pronator quadratus
• The palmar cutaneous branch supplies the lateral two-thirds of the palm

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In the palm

• Recurrent muscular branch, which supplies muscles of the thenar eminence, i.e., abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis
• Lateral terminal branch, which gives off digital nerves to supply both the sides of the thumb and the radial side of the index finger
  Note: The digital branch to the lateral side of the index finger also supplies the 1st lumbrical muscle.
• The medial terminal branch gives off digital nerves to supply the adjacent sides of the index and middle fingers and the adjacent sides of the index and little fingers the  2nd lumbrical muscle.

Median Nerve Applied Anatomy

The effects of the lesion on the median nerve depend on the site of the lesion.

Effects of Lesions of the Median Nerve