The ulnar nerve is a nerve that arises in the axilla from the medial cord of the brachial plexus, descends through the medial part of the upper arm to the back of the medial epicondyle, and passes between the heads of the flexor carpi ulnaris to enter the forearm.

 

Funny bone

The "funny bone" is really the ulnar nerve, which in most people is so little protected where it passes behind the internal condyle (the projection of the lower end of the humerus at the inner side) to the forearm, that it is often affected by blows on that part. The tingling sensation which is then felt to shoot down the forearm to the fingers has given rise to the name.

 

Course and relations of the ulnar nerve in forearm

The ulnar nervendescends in the medial part of the front of the forearm, lying upon the flexor digitorum profundus, under cover of the flexor carpi ulnaris. Near the pisiform bone it pierces the deep fascia at the lateral side of the flexor carpi ulnaris, and leaves the forearm by passing on to the front of the flexor retinaculum; and it ends on the retinaculum by dividing into two terminal branches – a superficial and a deep.

 

At the elbow, the ulnar nerve is separated from the ulnar artery by a wide interval; but, as they descend in the upper third of the forearm, the artery approaches the nerve, and, in the lower two-thirds, is closely applied to the lateral side.

 

Branches of the ulnar nerve in the forearm

The ulnar nerve gives off no branches till it reaches the forearm, where it supplies articular branches to the elbow joint; muscular branches which arise near the elbow for the flexor carpi ulnaris and the medial half of the flexor digitorum profundus; and the dorsal and palmar cutaneous branches.