[Music]
you've probably hit your elbow before
and felt a weird tingling shock run down
your arm in this video I'll try to
explain why this little glitch happens
and what it can tell us about how we
feel anything at all people call it the
funny bone but it's actually a nerve you
probably know that nerves are the body's
data cables but to really understand
what's going on here we're gonna have to
talk about the cells that make them up
neurons neurons are cells with special
electrical properties and they're
responsible for all the moving feeling
and thinking you do they come in many
shapes and sizes but in general they've
got a main body a bunch of dendrites and
one axon the dendrites can be thought of
as the inputs collecting electrical
signals and bringing them to the cell
body if the neuron gets enough input it
fires a pulse of energy down its axon
this signal can then be picked up by the
dendrites of other neurons
this can happen hundreds of times a
second and the resulting networks give
rise to all of your experiences so
that's a neuron broadly speaking we'll
need to go one level deeper to
understand the funnybone effect though
what are these pulses of energy the
electrical energy in a neuron exists
across its membrane the neuron actually
has tiny little pumps that move
electrically charged particles across
the membrane to maintain a gradient
you've probably heard these particles
and commercials for sports drinks
they're what make up electrolytes this
is one of their uses so we have this
imbalance like a little dam with energy
stored up across the membrane this is
called the resting potential when the
neuron wants to fire it just opens gates
in the membrane at the base of the axon
unless the particles rush through you
might imagine that they would pour down
the axon like a little electrical River
but that alone would be far too slow and
weak for the neurons purposes instead
there's a very clever system in place as
the electrical charge changes other
gates further along the axon are
triggered to open this process repeats
all the way down like a line of dominoes
and we have our pulse of energy called
the action potential this is how neurons
communicate okay so let's get back to
your elbow what you're hitting is a
nerve like I said a bundle of axons from
neurons communicating between your hand
and your brain these neurons in
particular are
possible for information coming from
your pinky finger and about half of your
ring finger and palm when you hit them
here physically squishing their axons
this allows for some particles to cross
their membranes it turns out that action
potentials don't need to start from the
base of the axon they can start anywhere
along it as long as there's a big enough
change in charge for the gates to open
so compressing a nerve is a bit like
hitting the middle of a row of dominoes
the chain reaction will actually go both
ways along it from the point of impact
now your brain at the other end is
listening to this nerve and giving you
sensations based on its activity but it
can't tell that these weird signals from
smacking your elbow aren't genuine
information about something that
happened to your hand you've effectively
bun tile to your brain it does the best
it can to interpret the signals and
that's when you get this bizarre tingly
buzzing sensation it's kind of your
brains version of the static of TV shows
when it's trying to turn the random
signals on an empty station into images
you can experience it yourself if you
hold out your arm and gently tap your
fingers between the two bones on your
elbow any tingling you feel in your hand
is actually a signal from your elbow
that your brain is misinterpreting you
can even feel the boundaries of where
your brain expects this nerve to have
information about only one side of your
ring finger will tingle so this annoying
experience of hitting your funny bone
actually provides a look under the hood
as your brain creates your experiences
from nerve signals the fact that your
nerves can go off willy-nilly if you hit
them might seem like a problem but most
of your nerves are well protected by
muscle and bone it can be a useful
feature - in fact specialized neurons
that are extra sensitive to pressure are
responsible for your ability to feel all
touch everything you've ever felt with
your pinky has been sent to your brain
along this nerve as electrical impulses
really anything you feel with your body
at all is your brain interpreting nerve
signals you can't feel what it's like to
be touched directly only what it feels
like to receive these inputs to your
brain this might seem like kind of a
meaningless philosophical distinction
but there's another glitch in your body
that can reveal the difference between
being touched and feeling touch as it
happens it has to do with your elbow
again this skin covering your elbow is
missing the special neurons that can
sense painful pressure if you extend
your arm and touch your elbow you'll be
able to feel that just fine
but if you give it a pinch you won't
feel anything at all there are no
neurons there to send messages to your
brain so you can't experience the
feeling of pressure remember to be
gentle again it's insensitive not
invulnerable so there you have it you
can feel without touch and touch without
feel our brains are excellent at making
sense of the world but perception is an
active process even feeling things with
your skin is fundamentally an active
interpretation that can sometimes go
wrong I hope you've enjoyed this video
thanks for watching and stay curious