Median nerve

Nerve: median nerve
Diagram from Gray's anatomy, depicting the peripheral nerves of the upper extremity, amongst others the median nerve
Latin	nervus medianus
Gray's	subject #210 938
Innervates	Anterior compartment of the forearm (with two exceptions), Thenar eminence, Lumbricals, skin of the hand
From	Lateral cord and Medial cord
MeSH	Median+Nerve

The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus.

The median nerve is formed from parts of the medial and lateral cords of the brachial plexus, and continues down the arm to enter the forearm with the brachial artery.

It originates from the brachial plexus with roots from C5, C6, C7, C8, & T1.

The median nerve is the only nerve that passes through the carpal tunnel. Carpal tunnel syndrome is the disability that results from the median nerve being pressed in the carpal tunnel.

Course

Course in the upper arm and cubital fossa

After receiving inputs from both the lateral and medial cords of the brachial plexus, the median nerve courses with brachial artery on medial side of arm between biceps brachii and brachialis. At first lateral to the artery, it then crosses anteriorly to run medial to the artery in the distal arm and into the cubital fossa.

Inside the cubital fossa the median nerve passes medial to the brachial artery, in front of the point of insertion of the brachialis muscle and deep to the biceps.

The median nerve gives off an articular branch in the upper arm as it passes the elbow joint.

Course and branches in the forearm

The median nerve arises from the cubital fossa and passes between the two heads of pronator teres. It then travels between flexor digitorum superficialis and flexor digitorum profundus before emerging between flexor digitorum superficialis and flexor pollicis longus.

The unbranched portion of the median nerve (which arises from the cubital fossa) innervates muscles of superficial and intermediate groups of the anterior compartment except flexor carpi ulnaris.

The median nerve does give off two branches as it courses through the forearm:

• The anterior interosseous branch courses with the anterior interosseous artery and innervates all the muscles of the deep group of the anterior compartment of the forearm except the medial (ulnar) half of flexor digitorum profundus and flexor carpi ulnaris muscle. It ends with its innervation of pronator quadratus.
• The palmar cutaneous branch of the median nerve arises at the distal part of the forearm. It supplies sensory innervation to the lateral aspect of the skin of the palm (but not the digits).

Branches in the hand

The median nerve enters the hand through the carpal tunnel, deep to the flexor retinaculum along with the tendons of flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus.

From there it sends off several branches:

• 1. Recurrent branch to muscles of the thenar compartment (the recurrent branch is also called "the million dollar nerve")^[1]. Here it provides motor innervation to opponens pollicis, abductor pollicis brevis and flexor pollicis brevis.
• 2. Digital cutaneous branches to common palmar digital branch and proper palmar digital branch of the median nerve which supply the:
  • a) lateral (radial) three and a half digits on the palmar side
  • b) index, middle and ring finger on dorsum of the hand
• 3. The median nerve supplies motor innervation to the first and second Lumbricals of the hand.

Distribution

Arm

The median nerve has no voluntary motor or cutaneous function in the (upper) arm. It gives vascular branches to the wall of the brachial artery. These vascular branches carry sympathetic fibers.

Forearm

It innervates all of the flexors in the forearm except flexor carpi ulnaris and that part of flexor digitorum profundus that supplies the medial two digits. The latter two muscles are supplied by the ulnar nerve (specifically the Muscular branches of ulnar nerve).

The main portion of the median nerve supplies the following muscles:

Superficial group:

• Pronator teres
• Flexor carpi radialis
• Palmaris longus

Intermediate group:

• Flexor digitorum superficialis muscle

The anterior interosseus branch of the median nerve supplies the following muscles:

Deep group:

• Flexor digitorum profundus (only the lateral half)
• Flexor pollicis longus
• Pronator quadratus

Hand

In the hand, the median nerve supplies motor innervation to the 1st and 2nd lumbrical muscles. It also supplies the muscles of the thenar eminence by a recurrent thenar branch. The rest of the intrinsic muscles of the hand are supplied by the ulnar nerve.

The median nerve innervates the skin of the palmar side of the thumb, the index and middle finger, half the ring finger, and the nail bed of these fingers. The lateral part of the palm is supplied by the palmar cutaneous branch of the median nerve, which leaves the nerve proximal to the wrist creases. This palmar cutaneous branch travels in a separate fascial groove adjacent to the flexor carpi radialis and then superficial to the flexor retinaculum. It is therefore spared in carpal tunnel syndrome.

The muscles of the hand supplied by the median nerve can be remembered using the mnemonic, "LOAF" for Lumbricals 1 & 2, Opponens pollicis, Abductor pollicis brevis and Flexor pollicis brevis. (NB: OAF are the thenar eminence)^[2]

Anatomic Anomalies

There are multiple naturally occurring anomalies of the median nerve.

• Bifurcation of the median nerve typically occurs after the nerve exits the carpal tunnel; however, in a small percentage (5%-10%) of individuals, the median nerve bifurcates more proximal in the carpal tunnel, wrist, or forearm.^[3]
• During gestation, a median artery that serves the hand retracts. However, in some individuals the median artery does not retract and follows the course next to the median nerve into the hand.
• Martin-Gruber anastomoses can occur when branches of the ulnar nerve cross-over in the forearm or wrist and merge with the median nerve to innervate portions of the hand.

Injury

Injury of median nerve at different levels cause different syndromes:

Above the elbow

• Injury of this nerve at a level above the elbow results in loss of pronation and a reduction in flexion of the hand at the wrist.

At the elbow

• Entrapment at the level of the elbow or the proximal forearm could be due to the pronator teres syndrome.
• Lesions of compression of the Median Nerve can also leads to Median Nerve Palsy

Within the forearm

• Injury to the anterior interosseous branch in the forearm causes the anterior interosseous syndrome.

At the wrist

• Injury by compression at the carpal tunnel causes carpal tunnel syndrome.
• Severing the median nerve causes median claw hand (also called the "Benedictine hand").
• In the hand, thenar muscles are paralyzed and will atrophy over time.
• Opposition and flexion of the thumb are lost.
• Sensory is lost:

Palm - 3 1/2 Fingers

Dorsal - Finger tips

• The thumb and index finger are arrested in adduction and hyperextension. This appearance of the hand is collectively referred as 'ape hand deformity'.^[1]

Additional images

• 

  Nervous system

• 

  Cross-section through the middle of upper arm.

• 

  Cross-section through the middle of the forearm.

• 

  Transverse section across distal ends of radius and ulna.

• 

  Transverse section across the wrist and digits.

• 

  The brachial artery.

• 

  Ulnar and radial arteries. Deep view.

• 

  The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front.

• 

  Cutaneous nerves of right upper extremity.

• 

  Diagram of segmental distribution of the cutaneous nerves of the right upper extremity.

• 

  Superficial palmar nerves.

• 

  Deep palmar nerves.

• 

  Front of right upper extremity, showing surface markings for bones, arteries, and nerves.

• 

  Brachial plexus

• 

  Brachial plexus with courses of spinal nerves shown

References

1. ^ ^{a b} "Anatomy Tables - Hand". http://anatomy.med.umich.edu/musculoskeletal_system/hand_tables.html. Retrieved 2008-01-06. 
2. ^ "Median nerve: Supply to hand". LifeHugger. http://mc.lifehugger.com/moc/963/Median_nerve_supply_to_hand. Retrieved 2009-12-14. 
3. ^ "Sonographic Representation of Bifid Median Nerve and Persistent Median Artery" Roll, SC. JDMS, 27: 89-94.

External links

• Duke Orthopedics median_nerve
• MeSH Median+Nerve
• Hand kinesiology at UK nerves/median.htm
• Atlas of anatomy at UMich hand_plexus - "Axilla, dissection, anterior view"

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.