How we might think more clearly about what is possibly a uniquely human experience: 'hitting the funny bone' (oleneural allision)

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Acknowledgement: I thank Elizabeth A. Carrie-Wilson for help in brainstorming a formal term in improvement of 'hitting the funny bone'.

Everyone knows what it is to 'hit your funny bone'.

It seems natural and inevitable that one will bump the point of the elbow, which is the proximal end of the ulna (the larger of the two bones of the forearm).

However, bumping a nerve in the region of the elbow is puzzling from a viewpoint of biological form and function. Furthermore, it may possibly be an experience unique to humans (Homo).

This phenomenon deserves a proper term, because

'Hitting the funny bone' is relevant to natural history, because

  • anatomy is generally subject to the biological principles of adaptation,
  • Homo sapiens is by far the most dexterous species on Earth, mainly owing to the neurological sophistication of the forearm, and
  • it is puzzling that the evolutionary process has allowed the persistence of a particular point of external vulnerability to a major nerve.

First, let us correct the lack of a technical term for the phenomenon. Then, let us begin to think about the adaptive significance of this ostensible flaw in the design of the human body.

The Latin term for elbow is 'cubitus'. The vulnerable section of the ulnar nerve runs through the cubital tunnel (https://en.wikipedia.org/wiki/Cubital_tunnel).

The cubital tunnel is located between two bony projections, one on a bone of the forearm and the other on a bone of the upper arm.

These are, respectively

(The cubital tunnel is not to be confused with the cubital fossa (https://teachmeanatomy.info/upper-limb/areas/cubital-fossa/), which is the 'pit of the elbow'.)

The word 'bump' conveys the correct meaning in this context, but is unsatisfactory, partly because of ambiguity between the noun and the verb, and partly because 'bumpage' is a particularly awkward word.

Therefore, the term 'allision' (https://en.wiktionary.org/wiki/allision#:~:text=allision%20(plural%20allisions),dashing%20against%20or%20striking%20upon.), although seldom used, is preferable.

On this basis, I might suggest that we replace 'hitting the funny bone' with 'cubital neural allision'.

However, this remains somewhat awkward.

The ancient Greek word for elbow is 'olene' (from which 'ulnar' is derived in the first place). Hence a more satisfactory new term might be OLENEURAL ALLISION.

In explanation of the peculiar vulnerability of the ulnar nerve, at the cubital tunnel, to accidental and passive impact, I hypothesise as follows.

Firstly, there is a principle that any evolutionary modification has both advantages and disadvantages. Thus, an adaptative syndrome as valuable as human dexterity can be expected to have some sort of 'downside'.

Ideally, the evolutionary process ensures that the whole anatomical configuration minimises this downside. However, some 'cost', in the sense of persistent risk and inconvenience, may be unavoidable.

Secondly, human dexterity depends partly on the particularly wide axial rotation of the forearm. This range of movement (in the action used to wield a screwdriver) is - in conjunction with opposability of the thumb - exceptional even among anthropoid primates.

This may necessitate a certain minimum distance between the bones to which the muscles attach at the elbow, particularly the medial epicondyle of the humerus and the head of the radius (https://www.ortho.wustl.edu/content/Patient-Care/3151/Services/Shoulder-Elbow/Overview/Elbow-Arthroscopy-Information/The-Anatomy-of-the-Elbow.aspx#:~:text=The%20elbow%20is%20a%20hinged,that%20form%20the%20joint%20capsule.).

For illustrations of the greater width of the head of the humerus in Homo than in chimpanzees (Pan) and baboons (Papio), please see Figures 1-2 and 1-3 in https://musculoskeletalkey.com/phylogeny/.

Thirdly, the exceptional dexterity of the human forearm demands three nerves of exceptionally large diameter. The ulnar nerve is one of these.

Please see:
https://upload.wikimedia.org/wikipedia/commons/5/51/Front_of_Sensory_Homunculus.gif
https://en.wikipedia.org/wiki/Cortical_homunculus#/media/File:Side-black.gif
https://en.wikipedia.org/wiki/Cortical_homunculus#/media/File:Rear_of_Sensory_Homunculus.jpg
https://upload.wikimedia.org/wikipedia/commons/0/0a/Sensory_and_motor_homunculi.jpg
https://en.wikipedia.org/wiki/Cortical_homunculus#/media/File:Sensory_Homunculus-en.svghttps://en.wikipedia.org/wiki/Cortical_homunculus#/media/File:Motor_homunculus.svg
https://upload.wikimedia.org/wikipedia/commons/d/df/Sensory_Homunculus-en.svg
https://en.wikipedia.org/wiki/Cortical_homunculus.

Putting these three lines of thinking together:

We seem to have a combination of a wide setting of the bony processes of the elbow (which produces a gap wide enough to warrant the term 'cubital tunnel') and a large ulnar nerve.

This 'spread of the bones' plus 'enlargement of the nerve' may make it unavoidable that some risk persists of accidental impact, when the arm occasionally bumps - at a certain angle - against objects in the environment.

Can readers improve on either the term 'oleneural allision', or my explanatory hypothesis?

Posted on 30 December, 2022 00:52 by milewski milewski

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