The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.

It originates from the brachial plexus, carrying fibers from the posterior roots of spinal nerves C5, C6, C7, C8 and T1.

The radial nerve and its branches provide motor innervation to the dorsal arm muscles (the triceps brachii and the anconeus) and the extrinsic extensors of the wrists and hands; it also provides cutaneous sensory innervation to most of the back of the hand, except for the back of the little finger and adjacent half of the ring finger (which are innervated by the ulnar nerve).

The radial nerve divides into a deep branch, which becomes the posterior interosseous nerve, and a superficial branch, which goes on to innervate the dorsum (back) of the hand.

This nerve was historically referred to as the musculospiral nerve.

Structure

thumb|right|300px|Radial nerve of the right axilla, posterior view

The radial nerve originates as a terminal branch of the posterior cord of the brachial plexus.

The radial nerve gives out muscular branches to supply the long head, medial head, and lateral head of triceps brachii muscles before and during its course in the radial sulcus. After it emerges out from the radial sulcus, it supplies the brachialis, brachioradialis and extensor carpi radialis longus.

  • The superficial branch of the radial nerve is widely separated from the radial artery in the upper one third of the forearm, closely related to radial artery in the middle third of the forearm, and in the lower third, it descends in the forearm under the tendon of brachioradialis. It crosses brachioradialis to enter posterior of forearm near the back of the wrist and supply dorsum of hand. It gives sensory supply to dorsal aspect of hand, dorsal aspect of thumb, index finger, middle finger and lateral side of ring finger except the nail beds, which are supplied by proper digital branches of median nerve.) pierces the supinator muscle, winds around the radius under the cover of supinator to reach posterior of forearm where it again pierces supinator and after which it is known as the posterior interosseous nerve. It pierces the posterior extensor muscles and comes to lie between superficial and deep muscles of the back of the forearm. At the lower border of extensor pollicis brevis, it passes deep to the extensor pollicis longus and then run on the posterior interosseous membrane. It continues to move along with posterior interosseous artery (a deep branch of common interosseous artery which is a branch of ulnar artery), and ends as a pseudoganglion below extensor retinaculum by supplying the wrist and intercarpal joints.

Function

The following are branches of the radial nerve (including the superficial branch of the radial nerve and the deep branch of the radial nerve/posterior interosseous nerve).

Cutaneous

thumb|Cutaneous innervation of the right upper extremity. Areas innervated by the radial nerve are colored in pink.

Cutaneous innervation by the radial nerve is provided by the following nerve branches:

  • Posterior cutaneous nerve of arm (originates in axilla)
  • Inferior lateral cutaneous nerve of arm (originates in arm)
  • Posterior cutaneous nerve of forearm (originates in arm)

The superficial branch of the radial nerve provides sensory innervation to much of the back of the hand, including the web of skin between the thumb and index finger.

Motor

thumb|Muscles of the posterior forearm. All the labelled muscles (that is, all the visible muscles except the ones on the dorsal hand and one at top right) are innervated by the radial nerve, and represent all muscles innervated by the radial nerve except for the [[supinator.]]

Muscular branches of the radial nerve:

  • Triceps brachii
  • Anconeus
  • Brachioradialis
  • Extensor carpi radialis longus

Deep branch of the radial nerve:

  • Extensor carpi radialis brevis
  • Supinator

Posterior interosseous nerve (a continuation of the deep branch after the supinator):

  • Extensor digitorum
  • Extensor digiti minimi
  • Extensor carpi ulnaris
  • Abductor pollicis longus
  • Extensor pollicis brevis
  • Extensor pollicis longus
  • Extensor indicis

The radial nerve (and its deep branch) provides motor innervation to the muscles in the posterior compartment of the arm and forearm, which are mostly extensors.

Clinical significance

Injury

Injury to the radial nerve at different levels causes different syndromes with varying motor and sensory deficits.

At the axilla

  • Common mechanisms of injury: Saturday night palsy,
  • Motor deficit:
  • Loss of extension of forearm, weakness of supination, and loss of extension of hand and fingers.
  • Presence of wrist drop, due to inability to extend the hand and fingers.
  • Sensory deficit: Loss of sensation

Additional images

<gallery widths="95" perrow="5">

File:Gray525.png|The brachial artery

File:Gray811and813.PNG|Cutaneous nerves of right upper extremity

File:Gray815.png|Superficial palmar nerves

File:Gray1235 (English).svg|Front of right upper extremity, showing surface markings for bones, arteries, and nerves

File:Gray1236.png|Back of right upper extremity, showing surface markings for bones and nerves

File:Brachial plexus 1.jpg|Radial nerve at newborn

File:Radial nerve 2.JPG|Radial nerve

File:Slide14yyy.JPG|Radial nerve

File:Slide10PPP.JPG|Radial nerve

File:Muscles of upper limb.(cross section - human cadaver).jpg|Muscles of upper limb. Cross section.

</gallery>

See also

  • Arcade of Frohse
  • Muscular branches of the radial nerve
  • Posterior brachial cutaneous nerve
  • Dorsal antibrachial cutaneous nerve
  • Superficial branch of the radial nerve
  • Deep branch of the radial nerve
  • Radial neuropathy
  • Radial tunnel syndrome

References

  • - "Axilla, dissection, anterior view"