M01.03.027 Median Nerve

The median nerve is a major peripheral nerve of the upper limb, crucial for motor and sensory functions. This article details its anatomical course, motor and sensory innervations, and clinical relevance with a focus on conditions such as carpal tunnel syndrome and nerve injuries.

Key Points

Feature	Description
Nerve Roots	C6–T1 (occasionally includes fibers from C5).
Motor Functions	Innervates forearm flexor and pronator muscles, thenar muscles, and lateral lumbricals.
Sensory Functions	Innervates the lateral palm and the lateral 3½ fingers (palmar surface).

Anatomical Course of the Median Nerve

Origin

Derived from: Medial and lateral cords of the brachial plexus.
Roots: C6–T1 (may include C5 in some individuals).

Pathway Through the Arm and Forearm

Axilla and Arm:
- Initially lateral to the brachial artery.
- Crosses the brachial artery halfway down the arm and moves medially.
Cubital Fossa:
- Enters the forearm by passing through the cubital fossa.
Forearm:
- Travels between the heads of the pronator teres muscle.
- Descends between the flexor digitorum profundus and flexor digitorum superficialis.
- Branches:
  - Anterior interosseous nerve: Supplies deep forearm muscles.
  - Palmar cutaneous nerve: Innervates the lateral palm.

Pathway Through the Hand

Enters via the carpal tunnel and divides into two branches:
- Recurrent branch: Supplies the thenar muscles.
- Palmar digital nerves: Supplies the lateral 3½ digits and lumbricals.

Motor Functions

Anterior Forearm Muscles

Layer	Muscles Innervated	Functions
Superficial	Pronator teres, flexor carpi radialis, palmaris longus	Forearm pronation, wrist flexion.
Intermediate	Flexor digitorum superficialis	Flexes middle phalanges.
Deep (via anterior interosseous nerve)	Flexor pollicis longus, pronator quadratus, lateral half of flexor digitorum profundus	Thumb flexion, distal phalanx flexion.

Hand Muscles

Branch	Muscles Innervated	Functions
Recurrent branch	Thenar muscles	Thumb opposition, abduction, and flexion.
Palmar digital nerves	Lateral two lumbricals	Flexion at MCP and extension at IP joints (index, middle fingers).

Sensory Functions

Branches and Innervation

Branch	Area Innervated
Palmar cutaneous nerve	Lateral palm (spared in carpal tunnel syndrome).
Palmar digital nerves	Palmar surface and fingertips of the lateral 3½ digits.

Clinical Relevance

Carpal Tunnel Syndrome (CTS)

Cause: Compression of the median nerve in the carpal tunnel.
Symptoms:
- Numbness, tingling, and pain in the lateral palm and fingers.
- Sparing of the palm (palmar cutaneous branch bypasses the tunnel).
- Weakness/atrophy of thenar muscles in chronic cases.
Tests:
- Tinel’s Sign: Tapping elicits pain in the median nerve distribution.
- Phalen’s Test: Flexed wrist position induces symptoms.
Treatment:
- Splinting, corticosteroid injections, or surgical decompression.

Lesions of the Median Nerve

Location of Injury	Mechanism	Effects
Elbow	Supracondylar fracture	Weak forearm pronation, loss of thumb flexion, hand of benediction.
Wrist	Lacerations near retinaculum	Thenar paralysis, weak thumb opposition, sensory loss in the lateral digits.

Points to Remember

Median nerve roots are C6–T1, occasionally including C5.
Carpal tunnel syndrome spares the palm due to the palmar cutaneous branch bypassing the tunnel.
Hand of benediction indicates a high lesion of the median nerve.
Physical tests like Tinel’s and Phalen’s are diagnostic for carpal tunnel syndrome.
Severe compression or lesions can lead to thenar muscle wasting.

References

TeachMeSeries Ltd (2024).
Comprehensive dissection images and 3D models for anatomy students available with premium access.

M01 Human Anatomy

Curriculum