Median nerve

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 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 (above) and brachialis (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. Inside the cubital fossa, the median nerve passes medial to the brachial artery. 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 (aponeurosis of biceps) and superficial the brachialis muscle. It crosses the ulnar artery (branch of brachial artery) while being separated by the deep head of the pronator teres. It then travels between the flexor digitorum superficialis (above) and flexor digitorum profundus (below). The median nerve is accompanied by the median artery (a branch of anterior interosseous artery) during this course. Then, about 5 cm above the flexor retinaculum (wrist), it emerges between the flexor digitorum superficialis (medially) and the flexor carpi radialis (laterally) into the hand. courses with the anterior interosseous artery and innervates flexor pollicis longus 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. In addition to its supply to muscles, this nerve also supplies the distal radioulnar joint and wrist joint. • 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. • 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. 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". 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 • Flexor carpi radialis • Palmaris longus Intermediate group: • Flexor digitorum superficialis muscle The anterior interosseus branch of the median nerve supplies these 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 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, thumb, middle finger, and half the ring finger, 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 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 • 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 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 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. Assessment When symptoms of tingling, numbness, pain, or muscle weakness occur, various assessments are conducted, including patient-reported subjective surveys, provocative tests meant to elicit or exacerbate symptoms, sensory and motor function tests, and diagnostic equipment. • Common patient-reported measures of symptoms and function are the Boston Carpal Tunnel Questionnaire (BCTQ) and its short version, the CTS-6, the Disabilities of the Arm, Shoulder, and Hand (DASH), and the Upper Limb Functional Index. • Provocative testing to examine free movement and gliding for the entire length of the median nerve is completed using an upper limb tension test. Phalen's, Tinel's, and Durkan's tests are used to assess compression at the wrist in the case of carpal tunnel syndrome. • Sensory testing is conducted across the dermatomes associated with sensory functioning of the median nerve using monofilaments or two-point discrimination instruments. Motor function tests focus on examining the use of the thenar muscles within the hand most affected by median nerve injury. Common functional tests include the evaluation of grip and pinch strength using dynamometry and gross and fine motor coordination ability using the Purdue pegboard, 9-hole peg test, and other assessment tools. • Electrodiagnostic testing using surface or needle electromyography is a widely used diagnostic assessment that can identify a specific location of nerve compression/injury or rule out other central nervous system conditions that could mimic a median nerve injury. Sonographic imaging can evaluate the median nerve's size, shape, and movement for comparison to normative values and identify locations or causes of nerve compression to support intervention selection, particularly within the carpal tunnel. Combinations of these assessments are useful for ruling out other conditions, identifying the location of nerve injury or compression, uncovering underlying causes of symptoms (such as tendonitis), determining the severity of the nerve injury, and developing individualized treatment plans based on patient characteristics. Such combinations of median nerve evaluations have been most widely validated in the assessment of carpal tunnel syndrome. ==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:Carpal-Tunnel.svg|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==