Everything about Ulnar Nerve totally explained
In
human anatomy, the
ulnar nerve is a nerve which runs near the
ulna bone. When someone says "hitting their funny bone", it's the aggravation of this nerve that's being referred to. The ulnar nerve is the largest unprotected nerve in the human body (meaning, unprotected by muscle or bone), and the only unprotected nerve that doesn't serve a sensory function (those nerves specifically meant to perceive changes in the environment, such as nerves in the skin).
Course
Arm
The ulnar nerve comes from the medial cord of the
brachial plexus, and runs inferior on the medial/posterior aspect of the
humerus down the arm, going behind the
medial epicondyle, through the
cubital tunnel, at the
elbow (where it's exposed for a few centimeters, just above the joint). Because of the mild pain and tingling throughout the forearm associated with an inadvertent impact of the nerve at this point, it's usually called the
funny bone. (It may also have to do with its location relative to the humerus, as the name "humerus" is a
homophone to the word "
humorous").
Forearm
It enters the anterior (front) side of the forearm and runs alongside the
ulna. There it supplies one and a half muscles (flexor carpi ulnaris & medial half of flexor digiti profundus). It soon joins with the
ulnar artery, and the two travel inferiorly together, deep to the
flexor carpi ulnaris muscle.
Here it gives off the following branches:
Hand
After its journey down the ulna, the ulnar nerve enters the palm of the hand. Unlike the
median nerve which travels below the
flexor retinaculum of the hand and through the
carpal tunnel, the ulnar nerve and artery pass superficial to the
flexor retinaculum via the
ulnar canal.
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:
In the hand, via the deep branch of ulnar nerve:
In the hand, via the superficial branch of ulnar nerve:
Cutaneous
The ulnar nerve also provides sensory innervation to the part of the hand corresponding to the fourth and fifth digits:
Palmar branch of ulnar nerve - anterior
Dorsal branch of ulnar nerve - posterior
Ulnar nerve entrapment
The Ulnar nerve can be trapped or pinched in various ways as it proceeds down the arm from the Brachial plexus to the ring and middle fingers. One common cause is cubital tunnel syndrome, where the tunnel runs the inner outside side of the elbow. Pinching of the nerve often causes tingling symptoms in the little and ring fingers. In some cases moderate to severe pain is experienced from pinching this nerve. Often such pins and needles sensations can be caused by sleeping wrongly on your arm, but sometimes the problems last for days. In severe cases, surgery is performed to move the nerve.
Further Information
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