The “funny bone” is not a bone at all, but one of the body’s major nerves. The common experience of “hitting your funny bone” is a sudden, sharp, electric shock-like feeling. This temporary, tingling sensation results from impacting a highly exposed nerve against an underlying bony structure at the elbow. This irritation affects a structure that controls both movement and sensation in the forearm and hand.
The Anatomy Behind the Name
The structure responsible for the intense sensation is the Ulnar Nerve, one of the three main nerves in the arm. It extends from the shoulder down to the hand, providing sensory information and motor control to specific muscles. The nerve gains its notoriety at the elbow because it passes through the cubital tunnel, a narrow channel.
This tunnel runs directly behind the prominent bony knob on the inner side of the elbow, called the Medial Epicondyle of the Humerus (the long bone of the upper arm). The Ulnar Nerve is unusually vulnerable here because it is not shielded by the typical layers of muscle, fat, or dense connective tissue. It lies very close to the skin, resting in a groove that allows it to be easily compressed. The popular nickname may stem from the word “humerus,” which sounds like “humorous,” or from the strange, “funny” feeling that results from the impact.
The Sensation: Why It Tangles and Hurts
When the elbow is struck, the Ulnar Nerve is momentarily crushed between the impact point and the unyielding surface of the Medial Epicondyle. This compression causes a sudden disruption of the electrical signals traveling along the nerve pathway. Since nerves transmit information through electrical impulses, this trauma causes the signals to become disorganized and confused.
The resulting sensation is temporary nerve dysfunction called paresthesia, which manifests as tingling, numbness, and sharp, shooting pain. Because the Ulnar Nerve supplies sensation to the ring finger and the entire pinky finger, the shock radiates instantly down the forearm and concentrates in these two digits. The feeling only lasts for a few seconds until the nerve recovers.
Protecting the Ulnar Nerve
The vulnerability of the Ulnar Nerve means protection involves avoiding direct impact and chronic compression. People often irritate this nerve not just by bumping it, but by habitually leaning on their elbows for extended periods while working at a desk. Sustained pressure or keeping the elbow flexed (bent) for a long time, such as while holding a phone or sleeping with the arm curled up, can also stretch and irritate the nerve.
If a mild bump occurs, the immediate tingling sensation usually subsides quickly on its own. However, if the pain, numbness, or tingling in the ring and pinky fingers persists, or if a person experiences chronic symptoms like weakness in the hand or difficulty with fine motor skills, a medical evaluation is warranted. These recurring symptoms suggest chronic nerve compression, which may require professional treatment.