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Ulnar Nerve Anatomy & Function

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Ulnar Nerve Anatomy & Function

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The ulnar nerve is the largest branch of the medial cord of the brachial plexus. It’s formed from the from the C8 and T1 nerve roots of the brachial plexus. The nerve courses along the medial arm and forearm, and then it passes into the wrist, hand, and fingers.

See Also: Brachial Plexus Anatomy

Ulnar Nerve Antony

It arises from the medial cord of the brachial plexus and contains fibers from the C8 and T1 nerve roots, although C7 may contribute some fibers. 

The ulnar nerve continues along the anterior compartment of the arm, and it passes through the medial intermuscular septum at the level of the coracobrachialis insertion. As the ulnar nerve passes into the posterior compartment of the arm, it courses through the arcade of Struthers, which is a potential site for its compression.

At the level of the elbow, the ulnar nerve passes posterior to the medial epicondyle, where it passes through the cubital tunnel. From there, the ulnar nerve passes between the two heads of the flexor carpi ulnaris origin and traverses the deep flexor–pronator aponeurosis. This aponeurosis is superficial to the flexor digitorum profundus, but deep to the flexor carpi ulnaris and flexor digitorum superficialis muscles.

The ulnar nerve enters the forearm by coursing posterior to the medial humeral condyle and passing between the heads of the flexor carpi ulnaris, before resting on the flexor digitorum profundus. It then continues distally to the wrist passing between the flexor carpi ulnaris and the flexor digitorum profundus muscles, which it supplies. 

Proximal to the wrist, the palmar cutaneous branch of the ulnar nerve arises. This branch runs across the palmar aspect of the forearm and the wrist outside of the tunnel of Guyon to supply the proximal part of the ulnar side of the palm. A few centimeters more distally to the tunnel, a posterior (dorsal) cutaneous branch arises and supplies the ulnar side of the dorsum of the hand, the posterior (dorsal) aspect of the fifth finger, and the ulnar half of the forefinger. 

Ulnar Nerve Function

Motor Function

The ulnar nerve supplies the flexor carpi ulnaris, the ulnar head of the flexor digitorum profundus, and all of the small muscles deep and medial to the long flexor tendon of the thumb, except the first two lumbricales, indicated by terminal branches in hand.

See Also: Forearm Muscles Anatomy & Function

Sensory Function

Its sensory distribution includes the skin of the little finger and the medial half of the hand and the ring finger.

See Also: Hand Nerves and Blood Supply
Ulnar Nerve Sensory Function

Ulnar Nerve Injury

The clinical features of ulnar nerve impairment include the following:

  1. Claw hand, resulting from unopposed action of the extensor digitorum communis in the fourth and fifth digits.
  2. An inability to extend the second and distal phalanges of any of the fingers.
  3. An inability to adduct or abduct the fingers, or to oppose all the fingertips, as in making a cone with the fingers and the thumb.
  4. An inability to adduct the thumb.
  5. At the wrist, flexion is weak and ulnar deviation is lost. The ulnar reflex is absent.
  6. Atrophy of the interosseous spaces (especially the first) and of the hypothenar eminence.
  7. A loss of sensation on the ulnar side of the hand and ring finger and, most markedly, over the entire little finger.
  8. Partial lesions of the ulnar nerve may produce only motor weakness or paralysis of a few of the muscles supplied by the nerve. Lesions that occur in the distal forearm or at the wrist spare the deep flexors and the flexor carpi ulnaris.
Ulnar Nerve - Claw hand

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