Median nerve – Course and Innervation

Origin

C5-T1 (Brachial plexus)

median nerve

Course

  1. Axilla: Starts in axilla (lateral or anterior to axillary artery)
  2. Arm: Runs along with brachial artery – initially lateral to it (in arm) and later medial to it (cubital fossa)
  3. Forearm: Enters the forearm between 2 heads of pronator teres (anterior interosseous nerve) and then travels between Flexor digitorum superficialis and Flexor digitorum profundus
  4. Wrist: Just above wrist, the nerve lies between Flexor digitorum superficialis and Flexor carpi ulnaris
  5. Hand: Enters the hand via carpal tunnel (Palmar cutaneous branch runs superficial to flexor retinaculum to supply thenar skin)

Motor innervation

Muscles supplied: 2 lateral lumbricals, 3 thenars, 3Ps (2 pronator and 1 palmaris) and 4 flexors.

  1. Superficial forearm: Pronator teres, Flexor carpi radialis, Palmaris longus (All superficial muscles except flexor carpi ulnaris)
  2. Intermediate forearm: Flexor digitorum superficialis
  3. Deep forearm: Flexor digitorum profundus (medial half supplied by ulnar nerve), Flexor pollicis longus, Pronator quadratus (by Anterior Interosseous Nerve or AIN)
  4. Hand: 1st and 2nd lumbricals, Oppones pollicis, Abductor pollicis brevis, Flexor pollicis brevis (All thenar muscles except adductor pollicis longus which is supplied by ulnar nerve)

Sensory innervation

  1. Palmar cutaneous branch: Lateral palm
  2. Digital cutaneous branch: Lateral 3 and 1/2 digits and palm on the palmar side and only fingertips on dorsal side

Clinical correlation

1. Martin-Gruber motor connection: occur in 17% of individuals between median and ulnar nerves resulting in variable innervations of intrinsic muscles.

2. Pronator syndrome: It presents with pain on volar aspect of distal arm and proximal forearm which may be increased by flexion of elbow or middle finger (FDS) against resistance. Entrapment neuropathy of median nerve in elbow; at 4 sites:

  • Ligament of struthers (connecting supracondylar spur to accessory origin of pronator teres)
  • Bicipital aponeurosis
  • Aponeurotic edges of deep head of pronator teres
  • Tendinous aponeurotic arch forming proximal free edge of radial attachment of Flexor Digitorum Superficialis (FDS)

3. Anterior interosseous nerve palsy: Weakness of pinch grip (due to involvement of flexor pollicis longus and flexor digitorum profundus of index finger) and no sensory symptoms (differentiating feature from pronator syndrome)

4. Injury:

pen test median nerve

  • At wrist level: Positive pen test (paralysis of abductor pollicis brevis) – unable to touch the object held above the thumb at right angle to palm and Ape thumb deformity (paralysis of abductor pollicis brevis) – adducted and laterally rotated thumb + Loss of opposition and abduction of thumb.
  • At elbow level: Above + Supinated forearm (pronators paralyzed) + Weak wrist flexion (Paralyzed long flexors except FCU and medial 1/2 FDP) + Adducted wrist (Paralyzed FCR and Intact FCU) + Loss of flexion of terminal phalynx of thum (FPL paralyzed) + Pointing index/Positive Oschner clasp/Benediction test (Paralysis of FDS and lateral 1/2 FDP = flexion of interphalangeal joint of index and middle fingers is lost)

pointing index median nerve

5. Carpal tunnel syndrome

Add Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.