Ulnar nerve

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Ulnar nerve
Brachial plexus 2.svg
Click image to enlarge - ulnar nerve is visible in lower left
Nerves of the left upper extremity.gif
Nerves of the left upper extremity. (Ulnar labeled at center left.)
Details
FromC8, T1 (branch from Medial cord)
Innervatesflexor carpi ulnaris
flexor digitorum profundus
lumbrical muscles
opponens digiti minimi
flexor digiti minimi
abductor digiti minimi
interossei
adductor pollicis
Identifiers
Latinnervus ulnaris
MeSHD014459
TAA14.2.03.040
FMA37319
Anatomical terms of neuroanatomy

In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body (meaning unprotected by muscle or bone), so injury is common. This nerve is directly connected to the little finger, and the adjacent half of the ring finger, innervating the palmar aspect of these fingers, including both front and back of the tips, perhaps as far back as the fingernail beds.

This nerve can cause an electric shock-like sensation by striking 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 bumping one's "funny bone". This name is thought to be a pun, based on the sound resemblance between the name of the bone of the upper arm, the "humerus" and the word "humorous".[1] Alternatively, according to the Oxford English Dictionary it may refer to "the peculiar sensation experienced when it is struck".[2]

Structure[edit]

Arm[edit]

The ulnar nerve originates from the C8-T1 nerve roots (and occasionally carries C7 fibres) which form part of the medial cord of the brachial plexus, and descends medial to the brachial artery, up until the insertion point of coracobrachialis muscle (middle 5 cm over the medial border of the humerus). Then, it pierces the medial intermuscular septum and enters the posterior compartment of the arm, accompanied by superior ulnar collateral vessels. It runs at the posteromedial aspects of the humerus, passing behind the medial epicondyle (in the cubital tunnel) at the elbow where it can be palpated by hand.[3]

Forearm[edit]

Ulnar nerve is not a content of the cubital fossa. It enters the anterior (flexor) compartment of the forearm between the two heads of flexor carpi ulnaris, lie along the lateral border of the flexor carpi ulnaris. The ulnar nerve runs between the flexor digitorum superficialis (laterally) and flexor digitorum profundus medially. Near the wrist, it courses superficial to the flexor retinaculum of hand, but covered by volar carpal ligament to enter the hand.[3]

In the forearm it gives off the following branches:[4]:700

Hand[edit]

Ulnar nerve enters the palm of the hand via the Guyon's canal, superficial to the flexor retinaculum and lateral to the pisiform bone.[3]

Here it gives off the following branches:[4]

Function[edit]

Ulnar nerve is also known as "musician's nerve" as it controls the fine movements of the fingers.[3]

Sensory[edit]

Cutaneous innervation of the right upper extremity. Areas innervated by the ulnar nerve are the areas on the hand colored in light blue.

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:

Motor[edit]

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.

Clinical significance[edit]

The ulnar nerve can suffer injury anywhere between its proximal origin of the brachial plexus all the way to its distal branches in the hand. It is the most commonly injured nerve around the elbow.[5] Although it can be damaged under various circumstances, it is commonly injured by local trauma or physical impingement ("pinched nerve"). Injury of the ulnar nerve at different levels causes specific motor and sensory deficits:

At the elbow

  • Common mechanisms of injury: Cubital tunnel syndrome, fracture of the medial epicondyle of the humerus (causing direct ulnar nerve injury), fracture of the lateral epicondyle of the humerus (causing cubitus valgus with tardy ulnar nerve palsy)
  • Motor deficit:
    • Weakness in flexion of the hand at the wrist, loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. (Note: Motor deficit is absent or very minor in cubital tunnel syndrome as the ulnar nerve is compressed in the cubital tunnel, rather than transected.)
    • Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the metacarpophalangeal joints, and flexion at the interphalangeal joints.
    • Weakness of adduction of the thumb, which may be assessed by the presence of Froment's sign.
  • Sensory deficit: Loss of sensation or paresthesiae in ulnar half of the palm and dorsum of hand, and the medial 1½ digits on both palmar and dorsal aspects of the hand

At the wrist

  • Common mechanism: penetrating wounds, Guyon canal cyst
  • Motor deficit:
    • Loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand.
    • Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the metacarpophalangeal joints, and flexion at the interphalangeal joints.
    • The claw hand deformity is more prominent with injury at the wrist as opposed to a lesion higher up in the arm, for instance, at the elbow, as the ulnar half of the flexor digitorum profundus is not affected. This pulls the distal interphalangeal joints of the 4th and 5th digit into a more flexed position, producing a more deformed 'claw'. This is known as the ulnar paradox.
    • Weakness of adduction of the thumb, which may be assessed by the presence of Froment's sign.
  • Sensory deficit: Loss of sensation or paresthesiae in ulnar half of the palm, and the medial 1½ digits on the palmar aspect of the hand, with dorsal sparing. The dorsal aspect of the hand is unaffected as the posterior cutaneous branch of the ulnar nerve is given off higher up in the forearm and does not reach the wrist.

In severe cases, surgery may be performed to relocate or "release" the nerve to prevent further injury.

See also[edit]

Additional images[edit]

References[edit]

  1. ^ Hendrickson, Robert A. The Facts on File Encyclopedia of Word and Phrase Origins (Facts on File Writer's Library). New York: Checkmark Books. p. 281. ISBN 0-8160-5992-6.
  2. ^ "Welcome to the new OED Online : Oxford English Dictionary". Dictionary.oed.com. Retrieved 2012-03-20.
  3. ^ a b c d e f g h i j k Krishna, Garg (2010). "8 - Arm". BD Chaurasia's Human Anatomy (Regional and Applied Dissection and Clinical) Volume 1 - Upper limb and thorax (Fifth ed.). India: CBS Publishers and Distributors Pvt Ltd. p. 91,110,111. ISBN 978-81-239-1863-1.
  4. ^ a b Ellis, Harold; Susan Standring; Gray, Henry David (2005). Gray's anatomy: the anatomical basis of clinical practice. St. Louis, Mo: Elsevier Churchill Livingstone. p. 726. ISBN 0-443-07168-3.
  5. ^ Selby, Ronald; Safran, Marc; O'brien, Stephen (2007). "Practical Orthopaedic Sports Medicine & Arthroscopy, 1st edition: Elbow Injuries". msdlatinamerica.com. Lippincott Williams & Wilkins.

External links[edit]