Why Does Hitting Your "Funny Bone" Feel So Horrible?

We've all been there: you accidentally knock your elbow against a hard surface, and a bizarre, unpleasant sensation shoots down your arm. It's a feeling so unique and jarring that it can take a moment to recover. But why does hitting what we commonly call the "funny bone" feel so incredibly weird?

The Elbow: A Complex Joint

The elbow is one of the most intricate joints in the human body, a meeting point for the humerus (the upper arm bone) and the two bones of the forearm. Nestled within this complex structure are three main nerves, one of which, the ulnar nerve, is the key player in the peculiar sensation we experience when we strike our "funny bone."

The Ulnar Nerve: Sensory and Motor Functions

The ulnar nerve is composed of both sensory and motor nerve fibers. It stretches from the spine down to the tips of the fourth and fifth fingers, providing sensation to these digits, as well as portions of the forearm and hand. When your little finger is injured, sensory receptors in the finger's tissues register the information and send electrical impulses up the ulnar nerve to the central nervous system, resulting in the perception of pain.

The Vulnerability of the Ulnar Nerve

Most nerves in your body are protected by muscle, fat, and bone. However, the ulnar nerve has a vulnerable point near the elbow. As it reaches the elbow, it passes beneath the medial epicondyle (the bony bump at the bottom of the humerus) and through the cubital tunnel, a passage formed by ligament and muscle tissue.

When you bend your elbow, the ulnar nerve is pressed against the medial epicondyle, displacing the protective tissue and bringing the nerve closer to the skin's surface. In this position, the ulnar nerve is covered only by skin and the cubital tunnel ligament tissue, making it one of the most exposed areas of nerve in your body.

The Peculiar Sensation: Direct Nerve Stimulation

When the exposed ulnar nerve is struck with sufficient force at the right angle, something unique happens. Instead of activating peripheral receptors that send electrical signals along the nerve, the nerve fibers are stimulated directly. This direct stimulation is what makes hitting your "funny bone" so different from other impacts.

Transient Paresthesia: Pins and Needles

The impact alters the ulnar nerve's signaling, possibly causing a surge of nerve signals. This leads to transient paresthesia, the intense pins-and-needles sensation that radiates down the arm. In rare cases, a hard enough strike can disrupt nerve signaling and blood flow, potentially leading to temporary loss of consciousness.

Ulnar Nerve Entrapment: A Chronic Concern

Repetitive bent-elbow activities can put pressure on the ulnar nerve over time, potentially leading to ulnar nerve entrapment. This condition occurs when the ulnar nerve becomes compressed and obstructed, most commonly within the cubital tunnel. Chronic ulnar nerve pain can result in persistent paresthesia and weakness in the forearm and hand.

Protecting Your Ulnar Nerve

To prevent ulnar nerve issues, doctors recommend mindful elbow usage. This includes:

• Stretching your arms
• Straightening your elbows
• Taking regular breaks to relieve pressure
• Promoting optimal blood flow to the ulnar nerve

By taking these precautions, you can help maintain the health of your ulnar nerve and avoid the unpleasant consequences of chronic compression.