Median nerve

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Nerve: median nerve
Nerves of the left upper extremity.gif
Diagram from Gray's anatomy, depicting the peripheral nerves of the upper extremity, amongst others the median nerve
Latin nervus medianus
Gray's p.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
Anatomical terms of neuroanatomy

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

The median nerve is formed from contributions from the lateral and medial cords of the brachial plexus, originating from ventral roots of C5, C6 & C7 (lateral cord) and C8 & T1 (medial cord).

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.

Structure[edit]

After receiving inputs from both the lateral and medial cords of the brachial plexus, the median nerve enters the arm from axilla at the inferior margin of the teres major muscle. It then passes vertically down and courses with brachial artery on medial side of arm between biceps brachii and brachialis. At first lateral to the artery and lies anterior to the elbow joint, 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. A branch to pronator teres may arise from the median nerve immediately proximal to the elbow joint.

Forearm[edit]

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(flexor) compartment except flexor carpi ulnaris.

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

Hand[edit]

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:

Variation[edit]

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.[2]
  • 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 median nerve cross-over in the forearm and merge with the ulnar nerve to innervate portions of the forehand.
  • Riche-Cannieu anastomoses can occur when there is connection between recurrent branch of the median nerve and deep branch of the ulnar nerve of the hand.

Function[edit]

Arm[edit]

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

Forearm[edit]

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:

Intermediate group:

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

Deep group:

Hand[edit]

The cutaneous innervation of the right hand. Areas supplied by the median nerve are colored green, the radial nerve red and the ulnar nerve blue.

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)[3]

Clinical significance[edit]

Injury[edit]

Injury of median nerve at different levels causes different syndromes with varying motor and sensory deficits.

Above the elbow

  • Common mechanism of injury: A supracondylar fracture.
  • Motor deficit:
    • Loss of pronation of forearm, weakness in flexion of the hand at the wrist, loss of flexion of radial half of digits and thumb, loss of abduction and opposition of thumb.
    • Presence of an ape hand deformity when the hand is at rest, due to an hyperextension of index finger and thumb, and an adducted thumb.
    • Presence of benediction sign when attempting to form a fist, due to loss of flexion of radial half of digits.
  • Sensory deficit: Loss of sensation in lateral 3½ digits including their nail beds, and the thenar area.

At the elbow

Within the proximal forearm: Anterior interosseous syndrome

  • Injury to the anterior interosseous branch in the forearm causes the anterior interosseous syndrome.
  • Common mechanisms: Tight cast, forearm bone fracture
  • Motor deficit: Loss of pronation of forearm, loss of flexion of radial half of digits and thumb.
  • Sensory deficit: None

At the wrist

  • Common mechanism: Wrist laceration
  • Motor deficit:
    • Weakness in flexion of radial half of digits and thumb, loss of abduction and opposition of thumb.
    • Presence of an ape hand deformity when the hand is at rest, due to an hyperextension of index finger and thumb, and an adducted thumb.
    • Presence of benediction sign when attempting to form a fist, due to weakness in flexion of radial half of digits.
  • Sensory deficit: Loss of sensation in lateral 3½ digits including their nail beds, and the thenar area.

Within the wrist: Carpal tunnel syndrome

  • Common mechanism: Carpal tunnel syndrome, an injury by compression in the carpal tunnel, without transection of the median nerve, due to overuse by activities such as keyboard typing and cooking.
  • Motor deficit:
    • Weakness in flexion of radial half of digits and thumb, weakness in abduction and opposition of thumb.
    • Absence of an ape hand deformity or when attempting to form a fist, the benediction sign, due to compression of the median nerve, as opposed to complete median nerve palsy.
  • Sensory deficit: Numbness and tingling in lateral 3½ digits including their nail beds but exluding the thenar eminence which is supplied by the superficial branch of the radial nerve.[4] Unlike in wrist laceration, there is no loss of sensation in the area of the central palm, as the palmar cutaneous branch runs above the flexor retinaculum, and is not affected in compression in carpal tunnel syndrome.

[1]

History[edit]

Additional images[edit]

See also[edit]

This article uses anatomical terminology; for an overview, see anatomical terminology.

References[edit]

This article incorporates text from a public domain edition of Gray's Anatomy.

  1. ^ a b "Anatomy Tables - Hand". Retrieved 2008-01-06. 
  2. ^ "Sonographic Representation of Bifid Median Nerve and Persistent Median Artery" Roll, SC. JDMS, 27: 89-94.
  3. ^ "Median nerve: Supply to hand". LifeHugger. Retrieved 2009-12-14. 
  4. ^ Figure 6.86, Moore Clinically Orientated Anatomy 7th Edition

External links[edit]