Origin and Course of Median Nerve

The median nerve is formed by the union of two roots in the axilla:

Lateral root — from the lateral cord of the brachial plexus, carrying fibres from C6, C7 (sometimes C5)
Medial root — from the medial cord of the brachial plexus, carrying fibres from C8, T1

Total root value: C6, C7, C8, T1 (occasionally C5).

The two roots embrace the third part of the axillary artery and unite on its lateral or anterior aspect to form the median nerve.

Course in the Arm

The median nerve descends through the arm lying lateral to the brachial artery in the upper part.
Near the insertion of coracobrachialis (middle of the arm), it crosses in front of the brachial artery (or occasionally behind it) to reach its medial side.
It continues distally on the medial side of the brachial artery to reach the cubital fossa.
The nerve gives off no branches in the arm (except occasionally a vascular twig).

In the cubital fossa, the median nerve lies medial to the brachial artery, behind the bicipital aponeurosis, and in front of brachialis.
It leaves the cubital fossa by passing between the two heads of pronator teres (superficial humeral head and deep ulnar head) to enter the forearm.
While passing between the two heads of pronator teres, it crosses in front of the ulnar artery, from which it is separated by the deep (ulnar) head of pronator teres.

After emerging between the heads of pronator teres, the median nerve passes deep to the fibrous arch of flexor digitorum superficialis (FDS).
It then runs down the forearm on the posterior surface of FDS, lying on flexor digitorum profundus (FDP).
It is accompanied by the median artery, a branch of the anterior interosseous artery.
About 5 cm above the flexor retinaculum, the nerve emerges from behind the lateral border of FDS and becomes superficial, lying between the tendons of flexor carpi radialis (laterally) and FDS (medially), overlapped by the tendon of palmaris longus.

The median nerve enters the palm by passing deep to the flexor retinaculum through the carpal tunnel, lying superficial to the flexor tendons.
Immediately distal to the flexor retinaculum, it terminates by dividing into a lateral and a medial division, which further split into muscular and digital branches.