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.