Everybody's Nerves are Different... "The Story of the Unexpected Nerve"

I like math.  1 + 1 = 2.  Always.  The teacher can't be too biased in grading this problem.  1 + 1 = 2. Period.

Medical students have it rough.  There are few absolutes for them.  There are 206 bones in the human body, right?  At some point, maybe in seventh grade, they told you that.  But is that true?  As for me, I have 208, as far as I know.  A few extra bones in my feet.  And this medicine will work for patient A, but not for patient B.

Going out on a limb,  I am going to say that muscles are probably similar from person to person.  Slightly different points of attachment, perhaps, but not too much variation.  (You medical people, feel free to chime in and correct me.)  From even my experiences, though, the nervous system can be markedly different from person to person.

Just for fun, look up "cutaneous innervation."  Click on your favorite picture.  You will see that some tattoo artist went crazy with a paint-by-number theme on a hapless victim.  Not really -- it just seems that way.  Each color represents an area of skin that is "serviced" by a particular nerve.  There are lots of nerve names.

We will look at the foot, my area of interest.  Specifically, the bottom of the foot.  This area is serviced by nerves called plantar nerves.  (Just like "plantar" warts are those on the bottom of the foot.  "Plantar" just refers to the bottom of the feet.)  Now, there are two main plantar nerves.  There is the lateral plantar nerve (orange innervation below), which services most of the bottom your foot along the pinky toe edge.  And there is the medial plantar nerve (blue innervation below, which services most of the bottom of your foot along the big toe side.  There are other nerves that service the white area, but I will ignore those for now.

Nerves branch, like a tree, until the smallest branches "stick" in your skin and send messages about touch, temperature, pain, etc.  And anatomy people like to name the big branches.  So, they name the branches found in most people.  For the foot, MOST cadavers studied in medical school have one main branch between each set of toes ("common digital nerves"), and then some lonely branches that just get half a toe (one side of the big toe, one side of the pinky -- "proper digital nerves."  They must be British.).  So, the lateral plantar nerve (orange) sends out one main branch to the outside of the pinky, and then one between the fourth and fifth toe (drawn in yellow, below).  The medial plantar nerve gets three common branches, and one proper (draw in red, below).  Feast your eyes on the beauty of digital artwork.

That is one way to do it.  Nature creatively has another way is to innervate that third "web space" (between toes 3 and 4) with a branch from the lateral plantar nerve and one from the medial.  They join to form a mutt nerve (this is term not found in medical textbooks, I'd wager -- green in my picture) like so:

That's lovely.  Well, when my patient's nerve got crushed, they took out that lovely green nerve there, and then we found out the skin really hadn't lost feeling, and there was still excruciating burning.  The anatomy charts totally failed us.  When we finally found the source of the original injury, it was something like the purple line on the picture below:

It was... THE UNEXPECTED NERVE.  An "extra" branch in that third webspace.  We are not sure where it originates.  The surgeon said it went medial (toward the center of the body), so it maybe came from the medial plantar nerve?

Anyway, I want to spread the word in case it saves years of someone else's life:  Nerves Are Different From Person To Person.  In a different post, I will cover that even the nerve bundles exiting the spine differ.  In peripheral nerves, there are crazy "communicating branches" that meld with other nerves.  Nerves branch at different places depending on the person.  Before they enter the tarsal tunnel.  After.  More main branches in one person, fewer in another.  I have heard that in the pubic area especially, there is extreme variation in which nerve innervates which area.  (All this makes me curious about the variation in muscle innervation, but I have not researched this area at all.)

I like math. 1 + 1 = 2.  This nerve mapping is called probability and statistics.  I hope they teach that in medical school, so they can find the next patient's "unexpected nerve."