Hitting your “funny bone” is a common experience that triggers a sudden, peculiar feeling that travels rapidly through your arm. It leaves many wondering about the precise biological reasons behind this distinctive and surprisingly painful jolt. This article explores the underlying science of this everyday phenomenon.
The Ulnar Nerve’s Vulnerability
The “funny bone” is the ulnar nerve, a superficial nerve originating from the C8 and T1 nerve roots in the neck. It extends down the arm and into the hand. While protected by muscles and fat for most of its length, the ulnar nerve becomes vulnerable as it passes through the cubital tunnel at the elbow. This narrow passageway is located on the inside of the elbow, behind the medial epicondyle. Here, the nerve lies very close to the skin with minimal cushioning, making it highly susceptible to direct impact or compression.
The Distinctive Sensation Explained
Hitting the ulnar nerve causes a unique and often intense sensation because the impact directly compresses the nerve. This compression temporarily disrupts the electrical signals that the nerve transmits between the hand and the brain. The ulnar nerve is responsible for both motor control and sensory information, including the ability to feel touch, temperature, and pain in the ring and little fingers, as well as coordinating fine hand movements. When these signals are interrupted, the brain receives a confused array of information, leading to the characteristic tingling, numbness, and sharp, electrical-like pain. This type of pain, originating directly from nerve irritation, feels different from the throbbing sensation of a typical bruise, which arises from tissue damage. The disruption is usually brief, with the sensation subsiding within seconds to a minute as the nerve recovers from the temporary compression.
The Origin of the “Funny Bone” Name
The colloquial term “funny bone” has two primary theories regarding its origin. One widely accepted idea is that the name stems from the peculiar, “funny” sensation experienced when the ulnar nerve is struck. Another theory connects the name to the humerus, the long bone of the upper arm that extends from the shoulder to the elbow. The ulnar nerve runs along the back of this bone at the elbow. Since “humerus” sounds similar to “humorous,” meaning funny, some believe the name “funny bone” is a playful pun based on this anatomical proximity. Both explanations contribute to the enduring and somewhat ironic name for this sensitive spot.