Bumping your elbow often causes a strange, intense sensation known as hitting your “funny bone.” This mix of discomfort and a tingling jolt can be surprising. While it feels like you’ve struck a bone, the sensation comes from something else entirely. This article explains the scientific reasons behind this unique phenomenon.
Unmasking the “Funny Bone”
The “funny bone” is not a bone, but the ulnar nerve. This nerve originates from nerve roots in the neck and is part of the brachial plexus, a network of nerves supplying the shoulder, arm, and hand. From its origin, the ulnar nerve travels down the arm, passing behind the medial epicondyle of the humerus, a bony prominence on the inside of the elbow.
The ulnar nerve descends along the forearm, running alongside the ulna bone, one of the two long bones in the forearm. It then proceeds into the wrist and hand, providing sensation and controlling many intricate hand movements. Its path close to bones and muscles makes it vulnerable to impact.
The Nerve’s Vulnerability
Hitting your “funny bone” hurts due to the ulnar nerve’s exposed position at the elbow. Here, the nerve passes through the cubital tunnel, a narrow passageway. This tunnel is formed by the medial epicondyle of the humerus, the olecranon process of the ulna, and a connecting fibrous band.
Within this cubital tunnel, the ulnar nerve lies superficially, close to the skin with minimal protective muscle or fat. Unlike most other nerves cushioned by tissues, the ulnar nerve at the elbow is exposed. When the elbow strikes a hard surface, the nerve compresses directly against the underlying medial epicondyle bone. This direct impact and compression causes the sudden, sharp pain.
The Unique Sensation
When the ulnar nerve is compressed at the elbow, the sensation is a mix of sharp pain, tingling, and numbness. This feeling often radiates down the forearm to the pinky finger and the adjacent half of the ring finger. This distinct distribution occurs because the ulnar nerve provides sensory innervation to these hand areas.
The tingling, often described as “pins and needles,” results from temporary disruption of the nerve’s signals by compression. While uncomfortable, the sensation is fleeting, as the nerve quickly recovers once pressure is removed. This combination of pain at the impact site and radiating sensation to the fingers is a direct consequence of the ulnar nerve’s anatomy and its role in transmitting sensory information.