The median nerve provides innervation to the forearm and hand.

Position. The median nerve is located at the level of the upper limb.

Even and mixed nerve. The median nerve is a pair and mixed nerve, that is, a nerve made up of sensory and motor nerve fibers.

Origin. The median nerve originates from the connection of the medial bundle and the lateral bundle of the brachial plexus, respectively originating from the vertebrae C8 to T1, and C5 to C7 (1).

Path. The median nerve runs down the arm 1. At the level of the anterior aspect of the forearm, branches start from the median nerve to reach the skin and the flexor muscles. It continues its journey to reach the hand and certain intrinsic muscles of the palm (1).

Branches. The median nerve divides into several branches:

• The muscular branches of the median nerve innervate the flexor muscles of the anterior compartment of the forearm: the palmar longus, the flexor carpi radialis, the flexor digitorum superficialis, the flexor digitorum longus, as well as the lateral half of the flexor digitorum. deep of the fingers and round pronator. These branches also innervate the intrinsic muscles of the lateral palm area, as well as the digital branches within the fingers (1).
• The cutaneous branches of the median nerve innervate the skin at two-thirds of the lateral aspect of the hand, the palm side, as well as the backs of the second and third fingers (1).

Wrist and finger movements. Innervation of the median nerve allows forearm pronation, wrist flexion, finger flexion, as well as thumb opposition (1).

Hand feeling. The median nerve allows the reception and transmission of sensitive information at the level of the hand (1).

Carpal tunnel syndrome. This syndrome corresponds to a compression of the median nerve at the level of the wrist, and more precisely at the level of the carpal tunnel (2) (3). This compression causes tingling, numbness and pain in the thumb, index and middle fingers. These sensations can continue and go up to the forearm and elbow. Compression of the median nerve also causes motor loss, i.e. a decrease in the strength of the hand and more particularly of the thumb (2). This condition can have different origins. It occurs in subjects performing repetitive movements such as secretaries, cashiers, etc. (1). It can also appear following a fracture or the development of osteoarthritis (2).

Symptomatic treatment. In order to reduce the discomfort, the subject can wear a splint during the night. Corticosteroid therapy may also be prescribed if the splint is not sufficient and symptoms persist (2).

Surgical treatment. Most often, surgery must be done to free the median nerve.

Physical examination. First, a clinical examination is carried out in order to observe and assess the sensory and motor signs perceived by the patient in the hand.

Medical imaging exam. Radiography can be used to confirm or further a diagnosis.

Electrophysiological exploration. The electromyogram makes it possible to study the electrical activity of the median nerve and to identify potential lesions.

Origin of the term carpal tunnel. The carpal tunnel owes its name to the carpal bones. Indeed, the carpal tunnel is the anatomical part of the hand and wrist between the carpal bones behind and the anterior annular ligament in front (2).