Median Nerve

Learning Objectives

After reading this post you will know:

  • Origin and root value of median nerve.
  • Course of median nerve.
  • Branches and structures supplied by median nerve.
  • Effects of lesion of median nerve.

Q. Describe the median nerve under the following headings:

  1. Origin and root value.
  2. Course
  3. Branches and structures supplied.
  4. Applied aspect.

A. Median nerve: 

  1.  Origin and root value: Arises in the axilla by two roots ( lateral and medial ) from the lateral and medial cords of brachial plexus.  Its root value is C5-T1 spinal segments .
  2. Course:
  •  Median nerve enters the anterior compartment of arm at the lower border of teres major.
  • In the arm, initially it lies lateral to the brachial artery, then crosses in front of the artery to reach its medial side.
  • Enters the cubital fossa where it lies medial to the brachial artery.
  • It leaves the cubital fossa by passing between the two heads of the pronator teres and gives off anterior interosseous nerve.
  • In the forearm , it passes behind the tendinous arch of flexor digitorum superficialis and runs downwards deep to the muscle.
  • 5 cm. proximal to flexor retinaculum it becomes superficial and lies lateral to the tendons of flexor digitorum superficialis .
  • It then enters the palm through the carpal tunnel (deep to flexor retinaculum) and divides into lateral and medial terminal branches.

       3. Branches and distribution:median nerve- branches and structures supplied by them

  • In the axilla and arm : no branches
  • In the cubital fossa:
    • Gives branches from its medial side to the all the superficial flexors  ( pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis) of the forearm except flexor carpi ulnaris.
  • In the forearm:
    • Anterior interosseous branch supplies 2 ½ muscles:
      • Flexor pollicis longus
      • Pronator quadrates
      • Lateral half of the flexor digitorum profundus.
  • Before entering carpal tunnel it gives off palmar cutaneous branch ( passes superficial to flexor retinaculum) which supplies skin over thenar eminence and lateral part of palm.
  • In the palm:
    • Lateral branch gives:
      • Motor branches :A recurrent branch that supplies thenar muscles ( abductor pollicis brevis, flexor pollicis brevis and opponens pollicis) except adductor pollicis.
      • Sensory branches: Three palmar digital branches.
  • Medial branch gives:
    • Sensory branches: Two palmar digital branches

The five palmar digital branches supply the skin of the palmar surface of lateral 3 ½ digits including the nail beds  and the skin on the dorsum of the distal phalanx .

cutaneous innervation by median nerve

4. Applied Anatomy:

  • Median nerve may get injured at the following sites:
    • At the elbow :
      • due to supracondylar fracture of humerus.
      • Entrapment of nerve between the two heads of pronator teres (pronator syndrome).
    • Injury to median nerve at this site results in:
      • Loss of pronation.
      • Weakened flexion at wrist.
      • Ape thumb deformity: Thum is laterally rotated and adducted. Opposition of thumb is not possible.
      • Thenar eminence is flattened
      • Benediction Attitude: when patient tries to make fist the index and the middle finger remain extended due to paralysis of the flexors of these two digits.
      • Sensory loss over the lateral half of the palm and lateral 3 ½ digits.
    • In the carpal tunnel : Refer to  post on carpal tunnel.

                       

 

 

 

 

 

 

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