Hitting one’s “funny bone” is a common experience, often causing a sudden jolt of tingling or pain. This sensation frequently prompts questions about its cause, which lies in the specific anatomy of the elbow. The widespread curiosity highlights a common misconception about what the “funny bone” truly is.
What the “Funny Bone” Really Is
Despite its name, the “funny bone” is not a bone at all; it is actually the ulnar nerve. This nerve is one of the three main nerves in the arm, originating from the neck and extending into the hand. At the elbow, the ulnar nerve passes through a specific groove on the humerus, the long bone of the upper arm. This location makes the nerve susceptible to external pressure.
The term “funny bone” likely derives from two aspects. One theory suggests it’s a play on words, as the upper arm bone is called the humerus, which sounds similar to “humorous.” Another explanation is the odd, “funny” feeling that occurs when the nerve is struck. This combination of wordplay and sensation cemented the informal name for this anatomical spot.
The Science Behind the Sensation
When the ulnar nerve at the elbow is struck, it produces a sensation ranging from tingling and numbness to sharp, electric-like pain. This occurs because, at this point, the ulnar nerve lacks the protective layers of muscle, fat, or bone that shield other nerves. It lies close to the skin’s surface, making it vulnerable to direct impact.
A sudden blow or compression to this exposed nerve disrupts the electrical signals traveling through it. The brain interprets this disruption as the characteristic “pins and needles” feeling or pain, which can radiate down the forearm and into the ring and little fingers. This temporary interference with nerve communication is why the sensation is immediate and intense, typically subsiding within minutes as the nerve recovers.
The Ulnar Nerve’s True Function
Beyond the fleeting sensation of hitting one’s “funny bone,” the ulnar nerve performs several functions for arm and hand movement. It is a mixed nerve, meaning it carries both motor and sensory information. For motor control, the ulnar nerve stimulates many small muscles within the hand, along with certain muscles in the forearm. These muscles enable fine motor skills, such as gripping objects, writing, and manipulating small items.
The ulnar nerve also provides sensory innervation, allowing for sensation in specific areas of the hand. It is primarily responsible for sensation in the little finger, half of the ring finger, and parts of the palm on the pinky finger side. Despite its vulnerability at the elbow, the ulnar nerve is a key part of the peripheral nervous system, contributing to hand dexterity and the perception of touch and temperature.