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), 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" .
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: 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: 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.
Translation of "Ulnar nerve"
German: Nervus ulnaris, French: Nerf ulnaire, Italian: Nervo ulnare, Hebrew: עצב הגומד, Japanese: 尺骨神経, Luxembourgish: Geckeg Knippchen, Dutch: Telefoonbotje, Polish: Nerw łokciowy, Portuguese: Nervo ulnar, Finnish: Kyynärhermo, Swedish: Nervus ulnaris.
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