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Median Nerve

Nervus medianus

For medical students2 min readUpdated 2026-10-10

The median nerve (nervus medianus) is a critical structure of the peripheral nervous system responsible for motor and sensory functions in the upper limb, notably innervating the majority of the anterior forearm and lateral palm. Understanding its branches and innervation zones is foundational for clinical neurology and surgery.

RootsThe median nerve is formed from nerve roots C₆–C₈ (along with contributions from C₅ and Th₁).
PalmProvides sensory innervation to the radial 2/3 of the palmar surface.
DigitsInnervates 3.5 digits on the hand: from the thumb to the lateral half of the ring finger.
AnastomosesSensory boundaries interface closely with the ulnar nerve (C₈–Th₁) territory.

Cutaneous Innervation of the Median Nerve

The median nerve originates from the spinal roots C₆–C₈. At the level of the hand, it divides into multiple branches, each supplying a distinct cutaneous zone. Knowing this topography is essential for localizing nerve lesions.

The main palmar branch of the median nerve (r. palmaris n. mediani) provides sensation to the radial 2/3 of the palm. Distally, the nerve gives rise to proper palmar digital nerves (nn. digitales palmares proprii), which supply the palmar skin of the following digits:

Additionally, the median nerve gives off common palmar digital nerves (nn. digitales palmares communes), which supply the first, second, and third web spaces.

Comparison with the Ulnar Nerve

To fully understand hand anatomy, the median nerve must be contrasted with the ulnar nerve (n. ulnaris), which arises from roots C₈–Th₁. Their territories are distinctly segregated, demonstrating the principles of segmental innervation.

While the median nerve covers the radial side, the palmar branch of the ulnar nerve (r. palmaris n. ulnaris) innervates the ulnar aspect of the palm. The proper palmar digital branches of the ulnar nerve supply the remaining areas:

The common palmar digital branches of the ulnar nerve travel through the fourth web space, completing the sensory supply of the hand.

Medial and Lateral Branches of Spinal Nerves

When reviewing the peripheral nervous system, it is also useful to note the branching patterns of posterior rami that supply the trunk and back musculature.

The medial branch targets deep structures. It innervates deep back muscles, specifically the multifidus muscles (mm. multifidi) and rotators (mm. rotatores). After passing through muscle layers, it terminates as the medial cutaneous branch (r. cutaneus medialis).

The lateral branch supplies more superficial structures, specifically the erector spinae muscles. It also terminates cutaneously as the lateral cutaneous branch (r. cutaneus lateralis).

Muscular Branches of the Trunk

The muscular branches (rr. musculares) of the thoracic nerves have a wide distribution, innervating multiple muscles of the chest wall and abdomen.

In the thoracic region, they supply:

The lower thoracic nerves (Th₇–Th₁₂) play a critical role in supplying the anterolateral abdominal wall, including the external and internal oblique abdominal muscles (m. obliquus externus et internus abdominis), transversus abdominis and rectus abdominis muscles (m. transversus et rectus abdominis), as well as the pyramidalis muscle (m. pyramidalis) and quadratus lumborum muscle (m. quadratus lumborum).

Mnemonic

To remember the digit distribution on the hand, think of 3.5. The median nerve supplies exactly three and a half digits (from the thumb to the radial half of the ring finger), while the ulnar nerve supplies the remaining one and a half (little finger and ulnar half of the ring finger).

Frequently asked questions

From which spinal nerve roots is the median nerve formed?

The median nerve is formed from the lateral and medial cords of the brachial plexus: the lateral root of the median nerve comes from the lateral cord, and the medial root comes from the medial cord. The brachial plexus arises from the anterior rami of C5–Th1.

What skin areas of the hand does the median nerve innervate?

The median nerve innervates the skin of the radial 2/3 of the palm, as well as the palmar surface and distal phalanges (dorsally) of the lateral digits.

Cutaneous innervation zones:

  • Palmar surface — skin of digits I, II, III, and the radial side of digit IV (including web spaces I–III).
  • Dorsal surface — skin of the distal (nail) phalanges of digits I, II, III, and the radial side of digit IV.
Which hand muscles does the median nerve innervate?

In the hand, the median nerve innervates the thenar muscles and some of the lumbricals.

These include:

  • Abductor pollicis brevis (m. abductor pollicis brevis).
  • Opponens pollicis (m. opponens pollicis).
  • Flexor pollicis brevis (m. flexor pollicis brevis — superficial head).
  • 1st and 2nd lumbricals (mm. lumbricales I et II), located on the radial side.
Which forearm muscles does the median nerve innervate?

In the forearm, the median nerve innervates most of the anterior compartment muscles (flexors and pronators), except for the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus.

Innervated muscles:

  • Pronator teres (m. pronator teres).
  • Flexor carpi radialis (m. flexor carpi radialis).
  • Palmaris longus (m. palmaris longus).
  • Flexor digitorum superficialis (m. flexor digitorum superficialis).
  • Flexor digitorum profundus (m. flexor digitorum profundus — lateral half).
  • Flexor pollicis longus (m. flexor pollicis longus).
  • Pronator quadratus (m. pronator quadratus).
Through which anatomical passage does the median nerve enter the hand?

The median nerve enters the hand through the carpal tunnel (canalis carpi). Within this narrow passage, the nerve lies superficially in the connective tissue beneath the flexor retinaculum (retinaculum musculorum flexorum) and superficial to the flexor tendons.

In which fascial groove does the median nerve travel in the forearm?

In the forearm, the median nerve travels in the median sulcus (sulcus medianus). It descends along the midline between the flexor digitorum superficialis and flexor digitorum profundus muscles. In the distal third of the forearm, the nerve becomes relatively superficial, making it vulnerable to lacerations at the wrist.

Which deep back muscles are innervated by the medial branch of posterior rami?

The medial branches of the posterior rami of thoracic spinal nerves carry both motor and sensory fibers. They innervate the following deep back muscles:

  • Multifidus muscles (mm. multifidi).
  • Rotator muscles (mm. rotatores).
Which spinal roots form the median nerve?

The median nerve originates from spinal roots C₆, C₇, and C₈ (with contributions from C₅ and Th₁ via the lateral and medial cords of the brachial plexus).

Which web spaces are supplied by the common palmar digital branches of the median nerve?

They supply the first, second, and third interdigital web spaces of the hand.

How is the innervation of the ring finger shared?

The ring finger has dual innervation: its radial half is supplied by the median nerve, and its ulnar half is supplied by the ulnar nerve.

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