Median Nerve

Median Nerve


MEDIAN NERVE 

  • The median nerve is also called labourer’s nerve.
  • The median nerve is a peripheral nerve originating at the brachial plexus from the lateral and medial cords of the ventral roots of C6, C7, C8 and T1.

MUSCLES SUPPLIED BY MEDIAN NERVE:

1) In the forearm

  • All the flexor muscles of the forearm, except the flexor carpi ulnaris & the medial half of flexor digitorum profundus to the ulnar two fingers.

These muscles are:

  1. Pronator teres
  2. Flexor carpi radialis
  3. Palmaris longus
  4. Flexor digitorum superficialis
  5. Flexor digitorum profundus[FDP] (lateral half)
  6. Flexor pollicis longus[FPL]
  7. Pronator quadratus

NOTE: FDP (lateral half), Pronator quadratus, FPL are muscles of deep compartment of forearm, & supplied by anterior interosseous branch of median nerve. Other muscles are supplied directly by median nerve.

2) In hand

  • Median nerve supplies:

i) Thenar muscles (except adductor pollicis):

  • Flexor pollicis brevis
  • Opponens pollicis
  • Abductor pollicis brevis
  • Adductor pollicis is supplied by ulnar nerve

ii) First two lumbricals                                                                            

SENSORY SUPPLY BY MEDIAN NERVE:

  1. Lateral two thirds of palm
  2. Lateral three & half fingers on palmar side & distal phalanx of lateral three & half digits on dorsal side.

MEDIAN NERVE INJURY

Etiology:

  1. In the arm– It is injured, though rarely by cut injury with a sharp object.
  2. At the elbow– It is commonly injured in the case of supracondylar fracture of humerus & dislocation of elbow.
  3. At the wrist The median nerve is often injured by cut injury due to knife or glass.
  4. In carpal tunnel– Pressure from a dislocated lunate bone can damage the nerve. Compression neuropathy (i.e. Carpal tunnel syndrome)is more common than injury.

Muscles examination of median nerve injury

  • From proximal to distal, the following muscles can be examined:-

1. Flexor pollicis longus:

  • The patient is asked to flex the terminal phalax of the thumb against resistance while the proximal phalanx is kept steady by the examiner.

2. Flexor digitorum superficialis & lateral half of flexor digitorum profundus:

  • If the patient is asked to clasp his hand, the index finger will remain straight, so-called ‘pointing index’.
  • This occurs because both the finger flexors, superficialis as well as profundus of the index finger are paralysed.

3. Flexor carpi radialis:

  • Normally, the palmar flexion at the wrist occurs in the long axis of the forearm.
  • In a patient with paralysed flexor carpi radialis, the wrist deviates to the the ulnar side while palmar flexion occurs.

4. Muscles of the thenar eminence:

  • Out of the three muscles of the thenar eminence, only two can be examined for their isolated action. There are as follows:-

i) Abductor pollicis brevis:

  • The action of this muscle is to draw the thumb forwards at right angle to the palm.
  • The patient is asked to lay his hand flat on the table with palm facing the ceiling.
  • A pen is held above the thumb & the patient is asked to touch the pen with tip of his thumb.
  • This is called ‘pen test’.

ii) Opponens pollicis: 

  • The function of this muscle is to appose the tip of the thumb to other fingers.
  • Apposition is a swinging movement of the thumb across the palm & not a simple adduction.
Exam Question
 
  • Median nerve is also known as labourer’s nerve
  • Formed from the branches of medial and lateral cord of brachial plexus.
  • Medial most structure in cubital fossa
  • Deep to pronator teres heads
  • Lateral to axillary artery in axilla
  • Passing deep to flexor retinaculum at wrist
  • seen in supracondylar # humerus
  • Median nerve supplies nail beds(anesthesized in surgeries related to nail bed)
  • Median nerve supplies Pronator teres of forearm
  • Median nerve supplies Opponens pollicis muscle of hand
  • Adductor pollicus will not be affected in median nerve palsy
  • Interosseous nerve  is the branch of median nerve
  • Pointing Index seen in median nerve palsy
  • Thenar muscle is wasted in median nerve palsy
  • Median nerve injury is Most common in lunate bone dislocation among all carpel bones
  • Median nerve injury at wrist is Tested by contraction of abductor pollicis brevis(pen test)
  • Ape thumb deformity observed in median nerve injury
  • Carpal Tunnel Syndrome seen in median nerve injury
  • Median nerve injury results in inability to pronate arm
Don’t Forget to Solve all the previous Year Question asked on Median Nerve

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