Ulnar nerve

Nerve: Ulnar nerve
Click image to enlarge - ulnar nerve is visible in lower left
Nerves of the left upper extremity. (Ulnar labeled at center left.)
Latin	nervus ulnaris
Gray's	subject #210 943
Innervates	flexor carpi ulnaris flexor digitorum profundis lumbrical muscles opponens digiti minimi flexor digiti minimi abductor digiti minimi interossei adductor pollicis
From	C8, T1 (branches off of Medial cord)
MeSH	Ulnar+nerve

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar nerve is the largest unprotected nerve in the human body (meaning, unprotected by muscle or bone),^{[citation needed]} and the only unprotected nerve that does not serve a purely sensory function (those nerves specifically meant to perceive changes in the environment, such as nerves in the skin). This nerve is directly connected to the little finger, and the adjacent half of the ring finger, supplying the palmar side of these fingers, including both front and back of the tips, perhaps as far back as the fingernail beds.

One method of injuring the nerve is to strike the medial epicondyle of the humerus from posteriorly, or inferiorly with the elbow flexed. The ulnar nerve is trapped between the bone and the overlying skin at this point. This is commonly referred to as hitting one's "funny bone." This name is thought to be a pun, based on the sound resemblance between the words "humerus" and "humourous" ^[1].

==Course==

Arm

The ulnar nerve comes from the medial cord of the brachial plexus, and descends on the posteromedial aspect of the humerus. It goes behind the medial epicondyle, through the cubital tunnel, at the elbow (where it is vulnerable to injury for a few centimeters, just above the joint).

Forearm

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

In the forearm it gives off the following branches:^[2]

• Muscular branches of ulnar nerve
• Palmar branch of ulnar nerve
• Dorsal branch of ulnar nerve

Hand

After it travels down the ulna, the ulnar nerve enters the palm of the hand. The ulnar nerve and artery pass superficial to the flexor retinaculum, via the ulnar canal.

The course of the ulnar nerve through the wrist contrasts with that of the median nerve, which travels deep to the flexor retinaculum of the hand and therefore through the carpal tunnel.

Here it gives off the following branches:^[2]

• Superficial branch of ulnar nerve
• Deep branch of ulnar nerve

Branches and innervation

Muscular

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

An Articular branch that passes to the elbow joint while the ulnar nerve is passing between the olecranon and medial epicondyle of the humerus.

• In the forearm, via the muscular branches of ulnar nerve:
  • Flexor carpi ulnaris
  • Flexor digitorum profundus (medial half)

• In the hand, via the deep branch of ulnar nerve:
  • hypothenar muscles
    • Opponens digiti minimi
    • Abductor digiti minimi
    • Flexor digiti minimi brevis
  • Adductor pollicis
  • Flexor Pollicis Brevis (deep head)
  • The third and fourth lumbrical muscles
  • Dorsal interossei
  • Palmar interossei

• In the hand, via the superficial branch of ulnar nerve:
  • Palmaris brevis

Cutaneous

The ulnar nerve also provides sensory innervation to the fifth digit and the medial half of the fourth digit, and the corresponding part of the palm:

• Palmar branch of ulnar nerve - supplies cutaneous innervation to the anterior skin and nails
• Dorsal branch of ulnar nerve - supplies cutaneous innervation to the posterior skin (except the nails)

Ulnar nerve entrapment

The ulnar nerve can be trapped or pinched as it proceeds from the brachial plexus to the fingertips. One common cause is cubital tunnel syndrome. In this syndrome, a tunnel on the medial side of the elbow traps the nerve.

Pinching of the ulnar nerve often causes paraesthesiae (tingling) in the fourth and fifth digits. Temporary paraesthesiae can be caused by sleeping while awkwardly placing weight on one's arm, or by cycling for extended periods of time. In severe cases, surgery is performed to move the nerve.

See also

• Radial nerve
• Axillary nerve
• Median nerve
• Musculocutaneous nerve

Additional images

Brachial plexus	Cross-section through the middle of upper arm.	Cross-section through the middle of the forearm.	Transverse section across distal ends of radius and ulna.
Transverse section across the wrist and digits.	The palmar aponeurosis.	The axillary artery and its branches.	The brachial artery.
Ulnar and radial arteries. Deep view.	The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front.	Cutaneous nerves of right upper extremity.	Diagram of segmental distribution of the cutaneous nerves of the right upper extremity.
Superficial palmar nerves.	Deep palmar nerves.	Front of right upper extremity, showing surface markings for bones, arteries, and nerves.	Back of right upper extremity, showing surface markings for bones and nerves.

References

External links

• Ulnar+nerve at eMedicine Dictionary
• Cubital Tunnel Support Forums
• 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
• Hand kinesiology at UK nerves/ulnar.htm
• Atlas of anatomy at UMich hand_plexus - "Axilla, dissection, anterior view"
• Overview at neuro.wustl.edu