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, where it may be compressed to cause carpal tunnel syndrome.

Course

Course in the upper arm and cubital fossa

After receiving inputs from both the lateral and medial roots of the corresponding 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 nerves 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 carpi radialis.

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 anterior compartment of the forearm except the flexor carpi ulnaris and the medial (ulnar) half of flexor digitorum profundus. Its 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]
• 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

The median nerve supplies motor innervation to the first and second lumbrical muscles.

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.

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.

Injury

Injury of median nerve at different levels cause different syndromes.

• 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.
• Entrapment at the level of the elbow or the proximal forearm could be due to the pronator teres syndrome.
• Injury to the anterior interosseous branch in the forearm causes the anterior interosseous syndrome.
• Injury by compression at the carpal tunnel causes carpal tunnel syndrome.
• Severing the median nerve can cause the hand of benediction.
• In the hand, thenar muscles are paralyzed and will atrophy over time. Opposition and flexion of the thumb are lost. 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

References

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.