Ulnar nerve

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In human anatomy, the ulnar nerve is a nerve which runs from the shoulder to the hand, at one part running near the ulna bone. It is the only exposed nerve in the human body (it is unprotected for a few centimeters at the elbow).

[edit] Course

The ulnar nerve comes from the medial cord of the brachial plexus, and runs inferior on the medial/posterior aspect of the humerus down the arm, going behind the medial epicondyle at the elbow. Because of the mild pain and tingling throughout the forearm associated with sudden compression of the nerve at this point, it is sometimes called the funny bone. (It may also have to do with its location relative to the humerus, as well as the fact that "humerus" is homophonic to the word "humorous").

It enters the anterior (front) side of the forearm, and runs alongside the ulna. There it supplies one and a half muscles (flexor carpi ulnaris & medial half of flexor digiti profundus). It soon joins with the ulnar artery, and the two travel inferiorly together, deep to the flexor carpi ulnaris muscle.

After its journey down the ulna, the ulnar nerve enters the palm of the hand. Unlike the median nerve which travels below the flexor retinaculum of the hand and through the carpal tunnel, the ulnar nerve and artery pass superficial to the flexor retinaculum via the ulnar canal.

[edit] Branches

The ulnar nerve has the following named branches:

• Palmar cutaneous branch of the ulnar nerve - arises about the middle of the forearm, and descends on the ulnar artery, giving off some filaments to the vessel. It perforates the palmar carpal ligament and ends in the skin of the palm, communicating with the palmar branch of the median nerve.
• Dorsal branch of the ulnar nerve (also dorsal cutaneous branch) - arises about 5 cm above the wrist from where the ulnar nerve splits into palmar and dorsal branches. The dorsal branch runs posteriorly beneath the flexor carpi ulnaris, perforates the deep fascia, and, running along the ulnar side of the back of the wrist and hand, divides into two dorsal digital branches; one supplies the ulnar side of the little finger; the other, the adjacent sides of the little and ring fingers. It also sends a twig to join that given by the superficial branch of the radial nerve for the adjoining sides of the middle and ring fingers, and assists in supplying them. A branch is distributed to the metacarpal region of the hand, communicating with a twig of the superficial branch of the radial nerve.
• Palmar branch of the ulnar nerve - arises about 5 cm above the wrist from where the ulnar nerve splits into palmar and dorsal branches. The palmar branch represents the continuation of the ulnar nerve as it crosses the flexor retinaculum of the hand on the lateral side of the pisiform bone, medial to and a little behind the ulnar artery. It ends by dividing into a superficial and a deep branch.
  • Superficial branch of the ulnar nerve - supplies the palmaris brevis and the skin on the ulnar side of the hand, and divides into a proper palmar digital nerve for the ulnar side of the little finger, and a common palmar digital nerve which gives a communicating twig to the median nerve and divides into two proper digital nerves for the adjoining sides of the little and ring fingers. The proper digital branches are distributed to the fingers in the same manner as those of the median nerve.
  • Deep branch of the ulnar nerve - accompanied by the deep branch of the ulnar artery, passes between the abductor digiti minimi and the flexor digiti minimi brevis. It then perforates the opponens digiti minimi and follows the course of the deep palmar arch beneath the flexor tendons. At its origin it supplies the hypothenar muscles. As it crosses the deep part of the hand, it supplies all the interosseous muscles and the third and fourth lumbricals. It ends by supplying the adductor pollicis and the medial head of the flexor pollicis brevis. It also sends articular filaments to the wrist-joint.

[edit] Innervation

The ulnar nerve and its branches innervate the following muscles in the forearm and hand:

• In the forearm:
  • Flexor carpi ulnaris
  • Flexor digitorum profundus (medial half)
• In the hand via the deep branch of the ulnar nerve:
  • Opponens digiti minimi - a hypothenar muscle
  • Abductor digiti minimi - a hypothenar muscle
  • Flexor digiti minimi brevis - a hypothenar muscle
  • Adductor pollicis
  • The third and fourth lumbrical muscles
  • Dorsal interossei
  • Palmar interossei
• In the hand via the superficial branch of the ulnar nerve:
  • Palmaris brevis

The ulnar nerve also provides sensory innervation to the part of the hand corresponding to the fourth and fifth digits, both anteriorly and posteriorly (via its palmar and dorsal cutaneous branches).

[edit] See also

• Radial artery
• Axillary nerve
• Median nerve

[edit] Additional images

Brachial plexus

Back of right upper extremity, showing surface markings for bones and nerves.

[edit] External links

• Dictionary at eMedicine Ulnar+nerve
• SUNY Figs 05:03-15 - "The major subdivisions and terminal nerves of the brachial plexus."
• SUNY Figs 07:04-04 - "Anterior view of the nerves, vessels, and superficial tendons that cross the left wrist."
• SUNY Figs 08:03-07 - "Transverse section through the carpal tunnel and distal row of the carpal bones."
• Duke Orthopedics ulnar_nerve
• Anatomy at MUN nerve/ulnerv
• Overview at neuro.wustl.edu

fr:Nerf ulnaire pt:nervo ulnar sv:Nervus ulnaris