| 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 #210 939 |
| 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 from Medial cord) |
| MeSH | Ulnar+nerve |
In human anatomy, the ulnar nerve is a nerve which 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, 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 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]
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The ulnar nerve originates from the C8-T1 nerve roots which form part of the medial cord of the brachial plexus, and descends on the posteromedial aspect of the humerus
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:[3]
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:[3]
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.
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:
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 or poor posture 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.
Severe entrapment or complete severing of the ulnar nerve can present clinically as an ulnar claw, or can be diagnosed by clinical tests, like card test,[4] Froment's sign, and so on.
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