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 and 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.
Structure 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
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 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:
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
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. 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. Here it provides motor innervation
to opponens pollicis, abductor pollicis brevis and superficial part of 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 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. Variation
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 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 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 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. Forearm
It innervates all of the flexors in the forearm except flexor carpi ulnaris and that part
of flexor digitorum profundus that supplies the 2nd and 3rd 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 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. Clinical significance
Injury 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
Entrapment at the level of the elbow or the proximal forearm could be due to the pronator
teres syndrome. 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. 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.
History Additional images
See also This article uses anatomical terminology;
for an overview, see anatomical terminology. References
This article incorporates text from a public domain edition of Gray's Anatomy.
External links Median_nerve at the Duke University Health
System's Orthopedics program Median Nerve at the US National Library of
Medicine Medical Subject Headings Hand kinesiology at the University of Kansas
Medical Center Atlas image: hand_plexus at the University
of Michigan Health System - "Axilla, dissection, anterior view"