Median

Question 1

Nerve roots:

Answer 1

C6 – T1.

Question 2

Motor functions:

Answer 2

Innervates the flexor muscles in the anterior compartment of the forearm (except the flexor carpi ulnaris and part of the flexor digitorum profundus, innervated by the ulnar nerve). Also supplies innervation to the thenar muscles and lateral two lumbricals in the hand.

Question 3

Sensory functions:

Answer 3

Gives rise to the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand.

Question 4

Anatomical Course

Answer 4

The median nerve is derived from the medial and lateral cords of the brachial plexus. It contains fibres from all five roots (C5-T1).

After originating from the brachial plexus in the axilla, the median nerve descends down the arm, initially lateral to the brachial artery. Halfway down the arm, the nerve crosses over the brachial artery, and becomes situated medially. The median nerve enters the anterior compartment of the forearm via the cubital fossa.

In the forearm, the nerve travels between the flexor digitorum profundus and flexor digitorum superficialis muscles. The median nerve gives rise to two major branches in the forearm:

Anterior interosseous nerve – Supplies the deep muscles in the anterior forearm.
Palmar cutaneous nerve – Innervates the skin of the lateral palm.

The median nerve enters the hand via the carpal tunnel, where it terminates by dividing into two branches:

Recurrent branch – Innervates the thenar muscles.
Palmar digital branch – Innervates the palmar surface and fingertips of the lateral three and half digits. Also innervates the lateral two lumbrical muscles.

Question 5

Motor Functions

Answer 5

The median nerve innervates the majority of the muscles in the anterior forearm, and some intrinsic hand muscles.

The Anterior Forearm

In the forearm, the median nerve directly innervates muscles in the superficial and intermediate layers:

Superficial layer: Pronator teres, flexor carpi radialis and palmaris longus.
Intermediate layer: Flexor digitorm superficialis.
The median nerve also gives rise to the anterior interosseous nerve, which supplies the deep flexors:

Deep layer: Flexor digitorum profundus, flexor pollicis longus and pronator quadratus.
In general these muscles perform pronation of the forearm, flexion of the wrist and flexion of the digits of the hand.
The Hand

The median nerve innervates some of the muscles in the hand via two branches. The recurrent branch of the median nerve innervates the thenar muscles – muscles associated with movements of the thumb. The palmar digital branch innervates the lateral two lumbricals – these muscles perform flexion at the metacarpophalangeal joints of the index and middle fingers

(The remaining muscles in the anterior forearm and hand are innervated by the ulnar nerve).

Question 6

Sensory Functions

Answer 6

The median nerve is responsible for the cutaneous innervation of part of the hand. This is achieved via two branches:

Palmar cutaneous branch – Arises in the forearm and travels into the hand. It innervates the lateral aspect of the palm. This nerve does not pass through the carpal tunnel, and is spared in carpal tunnel syndrome.
Palmar digital cutaneous branch – Arises in the hand. Innervates the palmar surface and fingertips of the lateral three and half digits.

Question 7

Clinical significance

Answer 7

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 3 1⁄2 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 3 1⁄2 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 3 1⁄2 digits including their nail beds but excluding the thenar eminence which is supplied by the palmar cutaneous branch of the median nerve .[4] 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.