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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 brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...
. The median nerve originates from the lateral and medial cords of the brachial plexus, and has contributions from ventral roots of C5-C7 (lateral cord) and C8 and T1 (medial cord). The median nerve is the only nerve that passes through the carpal tunnel.
Carpal tunnel syndrome Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
is the disability that results from the median nerve being pressed in the carpal tunnel.


Structure

The median nerve arises from the branches from lateral and medial cords of the brachial plexus, courses through the anterior part of arm, forearm, and hand, and terminates by supplying the muscles of the hand.


Arm

After receiving inputs from both the lateral and medial cords of the
brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...
, the median nerve enters the arm from the axilla at the inferior margin of the teres major muscle. It then passes vertically down and courses lateral to the brachial artery between
biceps brachii The biceps or biceps brachii ( la, musculus biceps brachii, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join t ...
(above) and
brachialis The brachialis (brachialis anticus), also known as the Teichmann muscle, is a muscle in the upper arm that flexes the elbow. It lies deeper than the biceps brachii, and makes up part of the floor of the region known as the cubital fossa (elbow p ...
(below). At first, it is lateral to the artery and lies anterior to the shoulder joint; it then crosses anteriorly to run medial to the artery in the distal arm and into the
cubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...
. Inside the
cubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...
, the median nerve passes medial to the
brachial artery The brachial artery is the major blood vessel of the (upper) 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 foss ...
. The median nerve gives off an articular branch to the elbow joint. A branch to
pronator teres The pronator teres is a muscle (located mainly in the forearm) that, along with the pronator quadratus, serves to pronate the forearm (turning it so that the palm faces posteriorly when from the anatomical position). It has two attachments, to ...
muscle arise from the median nerve immediately above the elbow joint.


Forearm

The median nerve continues in the cubital fossa medial to the brachial artery and passes between the two heads of the pronator teres, deep to the
bicipital aponeurosis The bicipital aponeurosis (also known as lacertus fibrosus) is a broad aponeurosis of the biceps brachii, which is located in the cubital fossa of the elbow. It separates superficial from deep structures in much of the fossa. Structure The bicip ...
(
aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...
of biceps) and superficial the brachialis muscle. It crosses the
ulnar artery The ulnar artery is the main blood vessel, with oxygenated blood, of the medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial ar ...
(branch of brachial artery) while being separated by the deep head of the pronator teres. It then travels between the
flexor digitorum superficialis Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest p ...
(above) and flexor digitorum profundus (below). The median nerve is accompanied by the
median artery The median artery is an artery that is occasionally found in humans and other animals. The prevalence was around 10% in people born in the mid-1880s compared to 30% in those born in the late 20th century, and 35% of people born as of 2020; a sig ...
(a branch of
anterior interosseous artery The anterior interosseous artery (volar interosseous artery) is an artery in the forearm. It is a branch of the common interosseous artery. Course It passes down the forearm on the palmar surface of the interosseous membrane. It is accompanied ...
) during this course. Then, about 5 cm above the flexor retinaculum (wrist), it emerges between the
flexor digitorum superficialis Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest p ...
(medially) and the
flexor carpi radialis In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and (radially) abduct the hand. The Latin ''carpus'' means wrist; hence flexor carpi is a flexor of the wrist. Origin and insertion The flexor carpi radialis is ...
(laterally) into the hand. The main trunk of the median nerve innervates the superficial and deep groups of the muscles in the anterior compartment of the forearm with the exception of
flexor carpi ulnaris The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. Structure Origin The flexor carpi ulnaris has two heads; a humeral head and ulnar head. The humeral head originates from the medial epicondyle ...
. The median nerve does this by giving off two branches as it courses through the forearm: *''Muscular branches'' are given off in the
cubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...
to supply
flexor carpi radialis In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and (radially) abduct the hand. The Latin ''carpus'' means wrist; hence flexor carpi is a flexor of the wrist. Origin and insertion The flexor carpi radialis is ...
,
palmaris longus The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; this number can vary in Afri ...
, and flexor digitorum superficialis. *The ''
anterior interosseous branch The anterior interosseous nerve (volar interosseous nerve) is a branch of the median nerve that supplies the deep muscles on the anterior of the forearm, except the ulnar (medial) half of the flexor digitorum profundus. Its nerve roots come from C8 ...
'' is given off in the upper part of the forearm, courses with the
anterior interosseous artery The anterior interosseous artery (volar interosseous artery) is an artery in the forearm. It is a branch of the common interosseous artery. Course It passes down the forearm on the palmar surface of the interosseous membrane. It is accompanied ...
and innervates
flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniqu ...
and the lateral half of flexor digitorum profundus (the ulnar half is supplied by ulnar nerve, as is the flexor carpi ulnaris muscle). It ends with its innervation of
pronator quadratus Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate (turn so the palm faces downwards) the hand. Structure Its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the a ...
. In addition to its supply to muscles, this nerve also supplies the distal radioulnar joint and wrist joint. The median nerve also gives off sensory and other branches in the forearm. The palmar cutaneous branch of the median nerve arises at the distal part of the forearm. It supplies sensory innervation to the thenar eminence of the palm and the central palm. Articular branches are given to the elbow joint and proximal radioulnar joint. Vascular branches supply the radial and ulnar arteries. Meanwhile, a communicating branch is given to the ulnar nerve.


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 superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest p ...
, flexor digitorum profundus, and
flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniqu ...
. From there, it is divided into recurrent muscular branch and digital cutaneous branch: * The muscular branch (also known as recurrent branch) supplies the thenar muscles ( opponens pollicis, abductor pollicis brevis, and superficial part of flexor pollicis brevis) *Digital cutaneous to the proper palmar digital branch and the common palmar digital branch: The proper palmar digital branch gives out three digital branches to the lateral one and a half digits (two digital branches to the thumb, one digital branch to the lateral side of the index finger). The digital branch to the index finger also supplies the first lumbrical. The common palmar digital branch divides further into two branches. Both the medial and lateral branches supply the second and third interdigital clefts with adjoining index, middle, and lateral half of ring finger. The lateral branch also supplies the second lumbrical.


Variation

The naturally occurring anomalies of the median nerve are: * 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 median nerve cross-over in the forearm and merge with the ulnar nerve to innervate portions of the forehand. * Riche-Cannieu anastomosis can occur when a connection exists between recurrent branch of the median nerve and deep branch of the ulnar nerve of the hand.


Function

The median nerve is the main nerve of the front of the
forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in an ...
. It supplies the muscles of the front of the forearm and muscles of the thenar eminence, thus controlling the coarse movements of the hand. Therefore, it is also called "labourer's nerve".


Arm

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 The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies internal organs, smooth muscle and glands. The autonomic nervous system is a control system t ...
.


Forearm

It innervates all of the flexors in the forearm, except
flexor carpi ulnaris The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. Structure Origin The flexor carpi ulnaris has two heads; a humeral head and ulnar head. The humeral head originates from the medial epicondyle ...
and that part of flexor digitorum profundus that supplies the fourth and fifth 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 these muscles: Superficial group: *
Pronator teres The pronator teres is a muscle (located mainly in the forearm) that, along with the pronator quadratus, serves to pronate the forearm (turning it so that the palm faces posteriorly when from the anatomical position). It has two attachments, to ...
*
Flexor carpi radialis In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and (radially) abduct the hand. The Latin ''carpus'' means wrist; hence flexor carpi is a flexor of the wrist. Origin and insertion The flexor carpi radialis is ...
*
Palmaris longus The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; this number can vary in Afri ...
Intermediate group: *
Flexor digitorum superficialis muscle Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest pa ...
The anterior interosseus branch of the median nerve supplies these muscles: Deep group: * Flexor digitorum profundus (only the lateral half) *
Flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniqu ...
*
Pronator quadratus Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate (turn so the palm faces downwards) the hand. Structure Its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the a ...


Hand

In the hand, the median nerve supplies motor innervation to the first and second 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 (volar) side of the
index finger The index finger (also referred to as forefinger, first finger, second finger, pointer finger, trigger finger, digitus secundus, digitus II, and many other terms) is the second digit of a human hand. It is located between the thumb and the mid ...
,
thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thum ...
, middle finger, and half the
ring finger The ring finger, third finger, fourth finger, leech finger, or annulary is the fourth digit of the human hand, located between the middle finger and the little finger. Sometimes the term ring finger only refers to the fourth digit of a left-ha ...
, and the nail bed. The radial aspect of the palm is supplied by the palmar cutaneous branch of the median nerve, which leaves the nerve proximal to the
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; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...
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.


Clinical significance


Injury

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


At the shoulder

* Injury can occur at the brachial plexus Above the elbow * Common mechanism of injury: a
supracondylar humerus fracture A supracondylar humerus fracture is a fracture of the distal humerus just above the elbow joint. The fracture is usually transverse or oblique and above the medial and lateral condyles and epicondyles. This fracture pattern is relatively rare in a ...
* Motor deficit: ** Loss of
pronation Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...
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 digits including their nail beds, and the thenar area 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 is a compression neuropathy of the median nerve at the elbow. It is rare compared to compression at the wrist (carpal tunnel syndrome) or isolated injury of the anterior interosseous branch of the median nerve ( anterior int ...
. Within the proximal forearm:
anterior interosseous syndrome Anterior interosseous syndrome is a medical condition in which damage to the anterior interosseous nerve (AIN), a distal motor and sensory branch of the median nerve, classically with severe weakness of the pincer movement of the thumb and index f ...
* Injury to the anterior interosseous branch in the forearm causes the
anterior interosseous syndrome Anterior interosseous syndrome is a medical condition in which damage to the anterior interosseous nerve (AIN), a distal motor and sensory branch of the median nerve, classically with severe weakness of the pincer movement of the thumb and index f ...
* Common mechanisms: tight cast, forearm bone fracture * Motor deficit: loss of
pronation Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...
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 may be likely, due to an hyperextension of index finger and thumb, and an adducted thumb. Nevertheless, an ape hand deformity is not a requirement for a carpal tunnel syndrome diagnosis. ** Presence of a 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 digits including their nail beds, and the thenar area Within the wrist: carpal tunnel syndrome * Common mechanism:
carpal tunnel syndrome Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
, 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 Cooking, cookery, or culinary arts is the art, science and craft of using heat to prepare food for consumption. Cooking techniques and ingredients vary widely, from grilling food over an open fire to using electric stoves, to baking in vario ...
* Motor deficit: ** Weakness in flexion of radial half of digits and thumb, weakness in abduction and opposition of thumb ** Presence 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 digits including their nail beds, but excluding the thenar eminence which is supplied by the palmar cutaneous branch of the median nerveFigure 6.86, Moore Clinically Orientated Anatomy 7th Edition Unlike in wrist laceration, sensation still occurs in the area of the central palm. Sensation is not lost because the palmar cutaneous branch runs above the flexor retinaculum, and is not affected in compression in
carpal tunnel syndrome Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
.


Additional images

File:Sobo 1909 554.png, Brachium seen anterolaterally, showing nerves and vasculature File:Sobo 1909 705-706.png, Antebrachium seen anteriorly, showing nerves and vasculature File:Braus 1921 165.png, Cross-section through the middle of upper arm (left), and middle of the forearm (right) File:Gray421.png, Transverse section across distal ends of radius and ulna File:Gray422.png, Transverse section across the wrist and digits File:Gray809.png, The right brachial plexus (infraclavicular portion) in the axillary fossa, viewed from below and in front File:Gray812and814.svg, Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. File:Gray815.png, Superficial palmar nerves File:Gray817.png, Deep palmar nerves File:Gray1235 (English).svg, Front of right upper extremity, showing surface markings for bones, arteries, and nerves File:Slide7FFFF.JPG, Median nerve File:Slide4MMMMM.JPG, Median nerve


See also


References


External links

* * * * - "Axilla, dissection, anterior view" {{Authority control Nerves of the upper limb