The stupidest nerve in the human body

Transcript

there appears to be a bit of a theme
emerging in that I always seem to be on
nights when I make these videos but as
the parent of two young children at home
I’ve actually been volunteering to do
on-call shifts at one of London’s
busiest hospitals it’s the only way I
get any rest but time is short so I’ll
get straight to the point here’s the
human body isn’t it amazing
no it’s idiotic your idiotic
specifically miss nerf not this note
that one’s fine not this nerve that
one’s amazing this nerve there are a
current laryngeal nerve it’s Battier
then a backwards retina let me tell you
why I don’t know in the next calls
coming in so I’ve chosen a topic that I
could do off-the-cuff because it’s a
favorite with evolutionary biologists in
a previous video we saw how evolution
has clumsily left remnants in your DNA
but you don’t even need a microscope to
be able to spot pointless leftovers in
the human body yes I know you don’t use
a microscope to look at genes it was
like a metaphor here is the tongue here
is the pharynx open it up and here is
the larynx here is a nerve that allows
you to speak the evidence for a designer
is incredibly weak part of the larynx is
innovated by the superior laryngeal
nerve which comes off the Vegas and goes
to the larynx in a fairly
straightforward common-sense route but
the other part of the larynx is supplied
by the recurrent laryngeal nerve on the
left look at the route it takes goes all
the way down into the chest loops under
the arch of the aorta and then back to
the larynx on the right side it goes
underneath the right subclavian in both
cases it takes a far longer route than
is necessary to borrow an engineering
technical term here I believe this could
be described as wack so was this a
one-off cock-up with humans definitely
not every tetrapod has the exact same
moronic setup including NBA camels also
known as giraffes whose recurrent
laryngeal gives a whole new meaning to
the expression
King the long way round so how did we
end up with this fresh nonsense well to
answer that we need to go back way back
back to when our brains were kind of on
our back because at this point in our
history we looked like some kind of fish
our primitive ancestor who may or may
not have tasted fantastic with matter
and chips didn’t have a larynx but they
did have the precursor that an organ
that would evolve into the larynx namely
the gills this is the international
symbol for gills in case you didn’t know
a set of aortic arches or blood vessels
spanned across the gills and connected
up to the heart from their tiny brain a
nerve also went in the most direct route
to the heart which passed the gills but
as life became more complex over the
subsequent millions of years body shapes
changed animals started having necks
moving their brains further away from
the heart instead of plotting a new
route to the larynx the recurrent
laryngeal was stuck behind the embryonic
vessel that would become our aorta cart
taking this manic loop instead of a much
shorter direct route I always thought
there was something fishy about you and
now I know I was right
when you were one month old one month
from conception that is you kind of
looks a bit like a primitive fish just
like a fish you had a set of aortic
arches instead of a single a water cart
that baby has you also had no neck but
you did have nerves including a
recurrent laryngeal nerve which started
its life taking a fairly sensible route
before it was yanked down but with the
heart into the chest as you developed
from a little blob into a baby taken to
its extreme this deviation achieves
frankly comical levels Mathew Adele
wrote a fantastic paper poking fun at a
tendency to trot out that giraffe as an
example with it’s two and a half meter
neck it’s got a recurrent laryngeal of
about 5 meters in length that’s nothing
where else says in comparison to the
sauropod whose dimensions truly were
next-level the largest sauropods had
about 14 meters between their brain and
their heart and as we know that
sauropods all had oranges we can
conclude that their recurrent laryngeal
nerves must have been
about 28 meters in length and the vast
majority of that was just an accident of
evolution for a final bonus factoid
remember that nerves are made up of
extremely long cells that run their
entire length so the axons that nerve
fibers in the recurrent laryngeal nerve
were a sauropod would be about the same
length as the cells in a blue whale’s
dorsal root ganglion making them
possibly the longest cells in the
history of the world VidCon last week we
were told to put a subscribe message in
our videos so but we were told maybe we
could offer incentives to our
subscribers now I don’t have a patreon
but if I did the top tier it would be
rewarded with a one-hour video of me
wearing my special super indoor
radiation-proof non sunglasses which are
literally made with LED they’re very
heavy and they protect my eyes from
x-ray so I don’t get cataracts and also
helped me being Superman in a staring
competition

Description

Evolution can’t slip into reverse and head back to the drawing board when it becomes apparent it’s ballsed things up. If someone designed this, I give them 1 star out of 5 and want my money back.

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References:
Wedel M. A Monument of Inefficiency: The Presumed Course of the Recurrent Laryngeal Nerve in Sauropod Dinosaurs https://www.researchgate.net/publication/268352345_A_Monument_of_Inefficiency_The_Presumed_Course_of_the_Recurrent_Laryngeal_Nerve_in_Sauropod_Dinosaurs
https://svpow.com/2011/05/23/the-worlds-longest-cells-speculations-on-the-nervous-systems-of-sauropods/

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Of course I learnt about the recurrent laryngeal nerve in the dissection room at medical school but I first appreciated its silliness when reading The Greatest Show on Earth by Richard Dawkins. It’s just one of the many examples of how evolution has resulted in quite daft anatomy and physiology.

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Tango de Manzana by Kevin MacLeod. Licensed under a Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/)
Source: https://incompetech.com/music/royalty-free/index.html?isrc=usuan1100404
Artist: http://incompetech.com/

Author: dhobson