Bumping your elbow often causes a sudden jolt and tingling sensation down your arm, commonly called hitting your “funny bone.” This feeling doesn’t come from striking a bone, but rather a highly sensitive nerve, prompting questions about its true cause.
The Ulnar Nerve: What You’re Actually Hitting
The “funny bone” is actually the ulnar nerve, one of the three main nerves in the arm. It originates from nerve roots in the neck and extends into the hand. Along its path, the ulnar nerve travels through a narrow passageway at the elbow called the cubital tunnel.
Within the cubital tunnel, the ulnar nerve passes behind a bony prominence on the inside of the elbow known as the medial epicondyle of the humerus. At this point, the nerve lies very close to the skin’s surface, lacking significant protection from muscle or bone. This superficial position makes the ulnar nerve particularly vulnerable to direct impact, leading to the characteristic sensation when the elbow is bumped.
Why The Sensation Occurs
When the ulnar nerve is struck, it gets compressed against the underlying medial epicondyle bone. This compression generates a burst of electrical signals that travel rapidly to the brain. The brain then interprets these signals as the distinct tingling, numbness, and sometimes sharp pain associated with hitting the “funny bone.”
The ulnar nerve provides sensory innervation to specific areas of the hand, including the pinky finger and the inner half of the ring finger. This is why the peculiar sensation often radiates to these fingers, creating a feeling of “pins and needles.” This temporary tingling or prickling sensation is medically termed paresthesia.
The Origin of “Funny Bone”
The term “funny bone” has a dual origin, stemming from both the sensation it produces and a linguistic play on words. One reason for the name is the unusual, “funny,” or peculiar sensation that occurs when the nerve is struck. Additionally, the nerve passes over the humerus bone, the long bone of the upper arm. The word “humerus” sounds similar to “humorous,” leading to a clever wordplay that cemented the name in common language.
When To Be Concerned
While hitting the “funny bone” is typically a harmless and temporary event, certain symptoms may indicate a more significant issue. If the numbness, tingling, or pain is prolonged, recurs without direct impact, or is accompanied by weakness in the hand, it could suggest ulnar nerve entrapment. This condition, also known as cubital tunnel syndrome, occurs when the ulnar nerve becomes compressed or irritated at the elbow. Persistent symptoms or any concerns regarding hand function warrant a medical consultation to determine the underlying cause and appropriate course of action.