The median nerve is a nerve

Nerve

A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

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

Brachial plexus

The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...

.

The median nerve is formed from parts of the medial and lateral cords of the brachial plexus

Brachial plexus

The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...

, and continues down the arm to enter the forearm with the brachial artery

Brachial artery

The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...

.

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

In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue...

. Carpal tunnel syndrome

Carpal tunnel syndrome

Carpal Tunnel Syndrome is an entrapment idiopathic median neuropathy, causing paresthesia, pain, and other symptoms in the distribution of the median nerve due to its compression at the wrist in the carpal tunnel. The pathophysiology is not completely understood but can be considered compression...

 is the disability that results from the median nerve being pressed in the carpal tunnel.

Course in the upper arm and cubital fossa

After receiving inputs from both the lateral and medial cords of the brachial plexus

Brachial plexus

The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...

, 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

Cubital fossa

The cubital fossa is the triangular area on the anterior view of the elbow of a human or other hominid animal. It is colloquially known as the "elbow pit".-Boundaries:...

.

Inside the cubital fossa

Cubital fossa

The cubital fossa is the triangular area on the anterior view of the elbow of a human or other hominid animal. It is colloquially known as the "elbow pit".-Boundaries:...

 the median nerve passes medial to the brachial artery

Brachial artery

The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...

, in front of the point of insertion of the brachialis muscle

Brachialis muscle

The brachialis is a muscle in the upper arm that flexes the elbow joint. It lies deeper than the biceps brachii, and is a synergist that assists the biceps brachii in flexing at the elbow...

 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
  Anterior compartment of the forearm
  The anterior compartment of the forearm contains the following muscles:* "E/I" refers to "extrinsic" or "intrinsic"....
  
   except the medial (ulnar) half of flexor digitorum profundus and flexor carpi ulnaris muscle. It ends with its innervation of pronator quadratus
  Pronator quadratus
  Pronator quadratus is a square shaped muscle on the distal forearm that acts to pronate the hand.As it is on the anterior side of the arm, it is innervated by a branch of the median nerve, the anterior interosseous nerve...
  
  .
• 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

Carpal tunnel

In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue...

, deep to the flexor retinaculum along with the tendon

Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

s 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"). 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
  Lumbricals of the hand
  The lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints and extend the interphalangeal joints.-Structure:There are four of these small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone...
  
  .

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

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

.

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

Ulnar nerve

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...

 (specifically the Muscular branches of ulnar nerve

Muscular branches of ulnar nerve

The muscular branches of ulnar nerve, two in number, arise near the elbow: one supplies the Flexor carpi ulnaris; the other, the ulnar half of the Flexor digitorum profundus. ....

).

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
  Flexor digitorum superficialis muscle
  Flexor digitorum superficialis is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints....
  
  

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
  Pronator quadratus
  Pronator quadratus is a square shaped muscle on the distal forearm that acts to pronate the hand.As it is on the anterior side of the arm, it is innervated by a branch of the median nerve, the anterior interosseous nerve...
  
  

Hand

In the hand, the median nerve supplies motor innervation to the 1st and 2nd lumbrical

Lumbrical

Lumbrical can refer to:* Lumbrical muscle * Lumbrical muscle...

 muscles. It also supplies the muscles of the thenar eminence

Thenar eminence

The thenar eminence refers to the group of muscles on the palm of the human hand at the base of the thumb...

 by a recurrent thenar branch. The rest of the intrinsic muscles of the hand are supplied by the ulnar nerve

Ulnar nerve

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...

.

The median nerve innervates the skin of the palmar side of the thumb

Thumb

The thumb is the first digit of the hand. When a person is standing in the medical anatomical position , the thumb is the lateral-most digit...

, the index

Index finger

The index finger, , is the first finger and the second digit of a human hand. It is located between the first and third digits, between the thumb and the middle finger...

 and middle finger

Middle finger

The middle finger or long finger is the third digit of the human hand, located between the index finger and the ring finger. It is usually the longest finger...

, half the ring finger

Ring finger

The ring finger is the fourth digit of the human hand, and the second most ulnar finger, located between the middle finger and the little finger. It is also called digitus medicinalis, the fourth finger, digitus annularis, digitus quartus, or digitus IV in anatomy.- Etymology :According to László A...

, and the nail bed

Nail bed

Nail bed can refer to:* Bed of nails, a device sometimes used in meditation and physics demonstrations* Bed of nails tester, a device used to test printed circuit boards* Fingernail region also known as the "quick"...

 of these finger

Finger

A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....

s. 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

Wrist

In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;...

 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

Mnemonic

A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...

, "LOAF" for Lumbricals 1 & 2, Opponens pollicis, Abductor pollicis brevis and Flexor pollicis brevis. (NB: OAF are the thenar eminence)

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.
• 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
  Pronation
  In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
  
   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
  Pronator teres syndrome
  Pronator teres syndrome is a compression neuropathy of the median nerve at the elbow.It is rare compared to compression at the wrist or isolated injury of the anterior interosseous branch of the median nerve .- Anatomy :The median nerve arises from the cubital fossa and passes between the two...
  
  .
• Lesions of compression of the Median Nerve can also leads to Median Nerve Palsy
  Median nerve palsy
  Injuries to the arm, forearm or wrist area can lead to various peripheral nerve disorders. One such disorder is median nerve palsy. If the median nerve is damaged, the ability to abduct and oppose the thumb may be lost due to paralysis of the thenar muscles. Various other symptoms can occur which...
  
  

Within the forearm

• Injury to the anterior interosseous branch in the forearm causes the anterior interosseous syndrome
  Anterior interosseous syndrome
  Anterior interosseous syndrome or Kiloh-Nevin syndrome I is a medical condition in which damage to the anterior interosseous nerve, a motor branch of the median nerve, causes pain in the forearm and a characteristic weakness of the pincer movement of the thumb and index finger.Most cases of...
  
  .

At the wrist

• Injury by compression at the carpal tunnel causes carpal tunnel syndrome
  Carpal tunnel syndrome
  Carpal Tunnel Syndrome is an entrapment idiopathic median neuropathy, causing paresthesia, pain, and other symptoms in the distribution of the median nerve due to its compression at the wrist in the carpal tunnel. The pathophysiology is not completely understood but can be considered compression...
  
  .
• Severing the median nerve causes median claw hand
  Hand of benediction
  The hand of benediction results from a severed Median nerve at the level of the elbow or upper arm. The ability to flex the digits 2–3 at the metacarpophalangeal joints, proximal interphalangeal joints and distal interphalangeal joints is lost. This is due to the loss of innervation of the lateral...
  
   (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
  Ape hand deformity
  Ape hand deformity is a deformity in humans who cannot move the thumb outside of the plane of the palm. It is caused by inability to oppose the thumb and the limited abduction of the thumb...
  
  '.