Behind the Brain

Ever hit your elbow in that just-right place and feel that weird combo of pain and tingling? Commonly referred to as hitting your “funny bone,” nothing feels funny except maybe how it leaves your arm numb and your fingers tingling. So, what’s happening when you hit this spot, and why does it feel so weird? Well, let’s examine more closely the interesting neuroscience of the funny bone.

The Anatomy of the “Funny Bone”

Despite its name, a funny bone is not exactly a bone, but rather your ulnar nerve, one of three principal nerves running down your arm. It courses from your neck down through your arm into your hand. Most of the hand muscles would normally be covered by the control of your ulnar nerve, as well as passing to the brain those sensations relating to ring and pinky fingers. As the ulnar nerve passes through the elbow, it does so via a very narrow space beneath the skin: the cubital tunnel. The area in which this nerve lies is somewhat uncovered; thus, that is why it is so easy to knock and cause such a strange, sharp sensation.

Why It Feels Funny (and Painful)

Well, when you hit your funny bone, what you are literally doing is compressing or irritating the ulnar nerve. The ulnar nerve then produces this sudden rush of these ‘mixed signals’ that reach your brain, which then perceives pain, tingling, and numbness. But why does it feel so special?

1. Dual Sensation: The ulnar is one of those few nerves which have both motor and sensory components. Thus, a bump may be followed by sharp pains, with tingling sensation-like electric current-simultaneously.
2. Pathway Confusion: The brain is not accustomed to a burst of input from the ulnar nerve all at once. It confuses the brain, which cannot deal with the excess input from the ulnar nerve, leading to this strange, almost comical response.
3. Referred Sensation: The tingling often extends to the pinky and ring fingers because those are the areas the ulnar nerve affects. This makes it feel as though the pain is radiating down your arm, although the source is at the elbow.

Why Is It Called the “Funny Bone”?

There are several theories on how the term “funny bone’s” originated. Most believe that it is a survival of the accidental pun on the “humerus,” the upper arm bone, having a similar pronunciation to “humorous.” Other people find it describes the peculiar almost humorous feeling the bumping of the nerve produces.

Ulnar Nerve Entrapment

Fortunately, most cases of a funny bone twitch are minor and the discomfort passes quite quickly. However, repeated irritation or chronic numbness could imply ulnar nerve entrapment. That would mean that the ulnar nerve has been compressed for an extremely long period through much flexing of the elbow and rest on a hard surface. In the case of such compression leading to chronic numbness of the ring and pinky fingers, weakness in hand and/or difficulty in holding anything tight.

Conclusion

It is not funny when you hit your funny bone, yet the neuroscience and story underlying the funny “bone” certainly is pretty funny. The funny bone is a classic example of how a misnomer, combined with misunderstood neuroscience can lead to myths that persist even in the 21st century. Furthermore, the funny bone is an example of how delicate and fragile our nervous system.