Median Nerve in Carpal Tunnel

In patient's with lacerations, sensation is assessed by examining light touch and/or two point discrimination.
The median nerve provides sensation palmarly to the thumb, index, long, and radial half of the ring finger.
The median nerve also provides the dorsal sensation around the fingernail and dorsum of the DIP joint. These areas are innervated by the dorsal branches of the digital nerves which originate from the median nerve.
Ultrasound measurement of the cross-sectional area of the median nerve can be used to support the diagnosis of carpal tunnel syndrome. Greater than 10 mm. suggests carpal tunnel syndrome.

Diagrams & Photos

Assessing median nerve sensation by examining light touch in palmar tip of the long finger.
Carpal tunnel anatomy: Carpal bones form the dorsal roof and the sides of the tunnel while the transverse palmar ligament forms the tunnel floor volarly. The tunnel contains nine flexor tendons and the median nerve.
Cutting the transverse carpal ligament to expose the contents of the carpal tunnel.

Key Points

The carpal tunnel is formed by the carpal bones and the transverse carpal ligament.
The radial side of the carpal tunnel is formed by the distal scaphoid and the trapezial ridge. The dorsal part is formed by the scaphoid, lunate, capitate, and hamate. The ulnar side is formed by the hook of hamate and pisiform.
On ultrasound the median nerve averages 6-10 mm wide at the entrance to the carpal tunnel.
In Section 9 the palmar cutaneous branch of the median nerve originates from the radial edge of the median nerve approximately 6 cm. proximal to the wrist flexion crease.