The term “funny bone” refers to a specific area on the back of the elbow that, when struck, produces a sudden, sharp pain followed by a distinct tingling that radiates down the arm. Although many people believe they are striking a bone, the uncomfortable feeling results from contact with a sensitive structure passing through the elbow joint. Understanding the anatomy reveals which structures are involved in this unique reaction.
The Anatomical Structure
The structure commonly mistaken for the “funny bone” is the lower end of the humerus, the long bone of the upper arm. The specific point that is struck is a bony prominence called the medial epicondyle, located on the inner side of the elbow. This section of the humerus forms part of the hinge joint connecting the upper arm to the forearm bones.
The Source of the Sensation
The source of the sensation is the ulnar nerve, one of the three main nerves in the arm. This nerve originates in the neck and travels down the arm, providing motor function to muscles in the forearm and hand. As it passes the elbow, the ulnar nerve temporarily leaves the protection of muscle and travels through a narrow passageway called the cubital tunnel. In this tunnel, the nerve runs directly over the groove of the medial epicondyle, making it exceptionally exposed. This superficial location allows a minor bump to directly compress the nerve against the hard bone.
The Unique Feeling Explained
The electric jolt and subsequent pins-and-needles sensation is a form of temporary paresthesia, or abnormal nerve function. Unlike most other nerves, the ulnar nerve lacks typical fatty tissue and muscle padding at this specific point on the elbow. When the nerve is suddenly compressed against the humerus, the impact disrupts its signaling pathway, causing it to send distorted messages to the brain. Since the ulnar nerve supplies feeling to the ring and pinky fingers, the sensation of pain and tingling often radiates directly down to these digits.
Why Is It Called the Funny Bone?
The common name “funny bone” is believed to have a dual origin, blending anatomical terminology with the resulting experience. The first source is a linguistic play on words, as the long bone of the upper arm is the humerus, which sounds similar to the word “humorous.” The second reason relates to the strange, or “funny,” feeling of the electric jolt that shoots down the arm immediately after impact.