Why does hitting your funny bone feel so horrible? - Cella Wright

Whatever you were doing, there was no way

to anticipate what came next. The back of your elbow smacked

against a hard surface and the impact sent a sensation

so distinctly disquieting shooting down your arm that it took

several moments to regain composure. So, why does hitting this spot

on your elbow— often referred to as your funny bone—

feel so weird? Well, to start, your elbow is one of the

most complicated joints in your body. It's where your upper arm bone,

the humerus, meets the two bones of your forearm. Three main nerves run through your elbow. One of them, the ulnar nerve, is

particularly relevant for our purposes. Your ulnar nerve is composed of both

sensory and motor nerve fibers. It extends from your spine to the tips

of your fourth and fifth fingers, providing them with sensation along with

swaths of your forearm and hand. So, say your little finger gets

crushed by a car door. Sensory receptors in your

pinky finger's tissues register that unfortunate information and send electrical impulses

up the ulnar nerve, which are then processed

in your central nervous system. This leads to the perception

of acute, sharp pain, followed by aching. So that's how your ulnar nerve

generally works. But your elbow has an anatomical quirk

that leaves your ulnar nerve vulnerable to getting activated in a different way. Along almost all of its length,

your ulnar nerve is protected, hidden beneath muscle, fat, and bone. Thankfully, this is generally true

of your nerves. But when your ulnar nerve

reaches your elbow, it runs beneath the bony bump

at the bottom of your humerus, named the medial epicondyle, and it passes through a tunnel of ligament

and muscle tissue called the cubital tunnel. When you bend your elbow, your ulnar nerve gets flattened

against the medial epicondyle and the protective tissue

in the area gets displaced, bringing the nerve especially close

to the skin's surface. In this position, the ulnar nerve

is covered only by skin and cubital tunnel ligament tissue, making it perhaps the longest area

of semi-exposed nerve in your body. So, when the area is struck at the

right angle with enough force, something interesting happens. Instead of the sensation simply activating

peripheral receptors that send electrical signals

along your ulnar nerve, the nerve's fibers are

stimulated directly. This is why hitting your so-called

funny bone hits different. The exact mechanisms aren't

yet fully understood. But the impact alters

the ulnar nerve's signaling, perhaps by causing a proliferation

of nerve signals, leading to that intense

pins-and-needles sensation called transient paresthesia, which radiates down the length

of your arm. In rare cases, whacks to this special spot have led to temporary loss

of consciousness, perhaps because a hard enough strike

could disrupt nerve signaling and blood flow. In addition to these more

immediately distressing moments, regular bent-elbow activities are

thought to put pressure on the ulnar nerve over time. Ulnar nerve entrapment is a relatively

common condition. It happens when the ulnar nerve becomes

compressed and obstructed, most commonly with the cubital tunnel. The result of this chronic ulnar nerve

pain can be persistent paresthesia, as well as weakness

in the forearm and hand. In the hopes of preventing

such conditions, doctors recommend conscientious

elbow usage. That includes stretching your arms

and straightening your elbows, and generally taking breaks that

help provide regular relief and maximal blood flow

to your ulnar nerve.

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