the human body is a remarkable machine
that can do all sorts of amazing things
we can dive tens of meters into the
ocean on a single breath or climb
thousands of meters toward the sky to
summit the tallest peaks but sometimes
our bodies also do stuff that's pretty
weird gross or just plain annoying over
the years we here at scishow have talked
about a lot of these other everyday
things that our bodies do and apparently
our patrons are big fans of these
episodes when we asked them to pick a
compilation topic they voted for us to
smush a bunch of why do we episodes into
one so here we go first you've probably
laughed at some point today and if not
well hopefully you will in the next 15
minutes or so at least we'll try to make
it happen anyhow laughing is just one of
those things all people do we laugh when
were amused and when we're anxious but
why what's the point of laughing let's
let Hank explain
you know it's like super funny laughter
laughter is a physiological response
that involves at least 15 facial muscles
the respiratory system the brains limbic
system and if the joke is really really
good even your tear duct thought
laughter doesn't always indicate happy
times it can actually be a sign that
something is seriously wrong with your
brain gelastic seizures or
uncontrollable and random laughter or
crying can indicate the presence of
brain tumors or other conditions like
pseudobulbar affect a neurological
condition that can affect stroke and
brain trauma survivors and MS patients
these conditions are sometimes called
emotional incontinence because the
sufferer can't control the outbursts
which often have no root and now they're
feeling and how we feel especially in
groups seems to be what laughing is all
about some laugh researchers and yes
they are things known as gel atala gists
think that much of our laughter is
rooted in strengthening social bonds
we're much more likely to laugh in a
group than we are alone and we tend to
laugh more easily around friends and
family that shared experience brings us
closer makes us feel part of the group
we also laugh to express relief or to
ease our nerves in stressful moments
researchers theorize that there are a
few specific reasons for laughing
first there's the incongruity theory
which maintains it's the element of
surprise that triggers laughter whether
it's an unexpected punchline or your
friend tripping over a throw rug so like
say you're watching people walk through
a room all day your brain registers this
as predictable and boring behavior then
your friend walks in trips on a rug and
drops a box of ping pong balls once
you're sure that your friend hasn't safe
falling on a bag of rusty knives you'll
find the fall hilarious because it was
sudden and unexpected and incongruous to
the string of people you'd seen safely
walking by and because ping pong balls
babies and little kids go for this kind
of laughter a lot they think really
simple unexpected things like my my face
is here it stared for five consecutive
hours it's still funny here like using a
banana as a telephone now if you're the
one who tripped on the throw rug you're
much more likely to laugh and surprised
if you see your friend laughing with you
this goes back to that shared laughter
as social bond thing you're probably
feeling pretty embarrassed intense but
are also relieved that you aren't hurt
that's where the relief theory comes in
laughing is like a mental mini break
your brain is constantly working taking
in all sorts of information and/or
around the body sometimes it just needs
a happy surprise this is particularly
handy in stressful moments the whole
Hollywood wisecrack in the middle of a
suspenseful scene phenomenon is
predicated on this idea when Han Solo is
in mortal danger he cracks a joke to
lighten the mood
he needs it chewy deeds it the audience
at the edge of their seats need it humor
helps us cope with stressful situations
it sort of recharges our brains to face
the task at hand scientists call this
releasing cognitive energy the rest of
us call it comic relief but now back to
you tripping on that throw rug if
everyone in the room is laughing at you
and none of them are your friends they
may be proving the superiority Theory of
laughter it means that they're laughing
at your misfortune and probably means
that they're kind of a bunch of jerk
faces superiority laughter still
promotes bonding and in us-versus-them
kind of way it doesn't show much
goodwill though
teenagers make fun of their parents and
you know each other and pretty much
everyone and so do lots of adults as
well but our teen years are usually
awkward and confusing and superiority
laughter may help ease some of that pain
so simply put we laugh hardest at what
we know best and at what stresses us out
the most and maybe that's why it's great
for you both physically and emotionally
it reduces the release of stress
hormones that jac those fight-or-flight
feelings it lowers blood pressure and
oxygenates your blood flow it even
increases your t-cell levels that help
your immune response and B cells that
produce antibodies also laughing a
hundred times is estimated to burn as
many calories as a 15-minute bike ride
so you see laughter is not the best
medicine but it's not a bad medicine
either
Wow there is a lot more to laughter than
I thought but of course laughter isn't
the only way we express emotions
physiologically for example when we're
embarrassed our cheeks turn bright red
whether we want them to or not but other
animals don't do this so why do we
here's michael with some ideas
in every culture and every ethnicity
around the world people blush but
animals don't and it's not just that
most animals faces are covered in fur
and feathers and stuff so we can't see
them blushing they actually don't blush
Charles Darwin called blushing the most
peculiar and most human of all
expressions which is awesome but why do
we blush physiologically we understand
it I mean we get the mechanics of why
your face turns red when Burnie sneaks
up behind you and pulls your pants down
in front of the whole rest of the
marching band
Bernice anyway your face turns red
because your sympathetic nervous system
kicks in that's the network of nerves
that controls your fight-or-flight
response when it's triggered it signals
the release of adrenaline and suddenly
your heart rate picks up and you start
breathing faster and then you're ready
to run away your pupils dilate and blood
rushes to your brain so you can take in
as much information as possible and your
blood vessels dilate in a process called
vasodilation to improve oxygen flow it's
basically the same effect you get from
warming up before a workout but in the
very hypothetical instance of my pants
being pulled down the blood vessels in
my face were responding specifically to
a chemical transmitter called adenylyl
cyclase it basically tells the blood
vessels in your face to let the
adrenaline in the weird thing is that
these same superficial blood vessels in
your face aren't usually affected by
sympathetic responses I mean we don't
blush when we're scared if we did that
might be a sign that blushing served
some sort of survival purpose but it
only happens when we're not actually in
danger
so like why well some scientists believe
that blushing evolved as a social
survival trait when you blush then the
person who's angry you can see that
you're really sorry and the person who's
laughing at you can see that you're
visibly embarrassed if that sounds weird
just think about the last time your dog
chewed on the furniture then rolled onto
its back when you got mad lots of
animals have evolved this sort of
behavior so they can say hey whoa I
messed up I feel terrible and it's
really hard to stay mad at your dog when
it does that that's how you know it's
working we may never know for sure why
blushing became a thing but it could
just be our way of saying sorry for
chewing on the furniture
huh I never thought of it that way but
blushing is a social signal does make
sense especially when you consider how
often our bodies involuntarily do things
that are considered offensive like we
burp and fart a lot and while I get that
we all have gas why do we have to expel
so much of it all the time
here is Hank to explain
formerly referred to is belching in
flatulence these two often lampooned
bodily functions actually share a common
cause swallowed air every time you
swallow you take in some air but you can
swallow even more air than normal if you
eat or drink too quickly chew gum smoke
drink carbonated beverages or even wear
loose fitting dentures now the majority
of swallowed air comes back up in the
form of burps as the air builds up in
the upper portion of the stomach
it causes stretching that eventually
triggers the lower esophageal sphincter
to relax the result is air escaping up
the esophagus into the mouth where the
sound and smell of the burp depends on
how much coke you just chugged babies in
particular are big burp errs especially
for their small size mostly because they
tend to go up in too much air while
nursing and because young digestive
systems haven't developed to the point
where babies can easily burp on their
own it's up to mom and dad to Pat their
backs help get those gas bubbles out but
for babies and adults what about the air
that isn't burped out well it passes
from the stomach into the small
intestine and later the large intestine
along the way as it passes through the
gastrointestinal tract that air mixes
with the products of some good old back
to your fermentation that's going on
your guts and fermentation is the result
of carbohydrates like sugars and
starches that can't be digested by
enzymes in the small intestine some
foods that include these hard to digest
starches include cabbage cauliflower
beans and bran which explains why you
may feel excessively gassy after that
big bowl of chili when those undigested
and carbs reach the colon and the lower
intestines bacteria take over the
by-product is a combination of gases
that include carbon dioxide hydrogen
methane even hydrogen sulfide a stinky
one that mix of gases plus the air that
you've swallowed is what makes its way
through the large intestine to the anus
where it is expelled of course everyone
has different amounts of various species
of bacteria and yeasts working away in
their guts but I'm sure you're dying to
know so I'll just tell you the average
human toot contains roughly 59% nitrogen
21% hydrogen 9% co2
7% methane and 4% oxygen if that last 1%
in the form of hydrogen sulfide and
other sulfur compounds that is the most
potent in terms of producing those
notorious unpleasant rotten egg smells
well some of these chemicals are
produced by bacteria
you're got eating sulfur-rich foods like
eggs and onions and beans that doesn't
help on the smelly front
well now I know more than I ever needed
to about the composition of firts thanks
Hank while we're on the subject of
expelling air though sneezing is another
kind of annoying thing our bodies do and
the reason might seem obvious but
expelling pathogens from our noses is
only a part of the answer to why we
sneeze as Michael explains
everyone everywhere occasionally sneezes
it's something that humans and even some
animals like cats and dogs and chickens
just do but why why do we sneeze if your
answer is that it's our noses way of
getting rid of irritants and excess
mucus you're right but only partly the
scientists have long thought that
sneezing technically known as stern
mutation is a reflex when irritants like
dust dander germs or pollen get into
your nose your brain sends out a signal
to get rid of it that same signal goes
out if an excessive amount of mucus is
hanging out in there to say if you have
a cold
this signal triggers a deep breath which
you hold in your lungs for a moment and
while you're holding your breath your
chest muscles clench and pressure builds
your tongue is forced to the roof of
your mouth and you breathe out fast
through your nose in the form of a
sneeze that is the old short and still
correct answer to the question why do we
Sneed
according to a paper published in 2012
in the journal fathom there's a little
more to it than that and it all has to
do with cilia the tiny hairlike paddles
that line our noses and sinuses in the
study a group of researchers from the
university of pennsylvania basically
grew a tiny nose they took cells from
the nostrils of several healthy adults
and grew them in an incubator for a few
weeks until the cells had formed the
same type of lining that's in your sinus
complete with cilia then to mimic a
sneeze the scientists puffed air onto
the lining they noticed that the bursts
of air triggered the celia to kick into
high gear moving back and forth
repeatedly for up to several minutes
after the trick sneeze so why were they
so active for so long any potential
irritants would have been cleared out
already
well the triggered cilia were acting as
a broom basically resetting the entire
nasal environment not just the parts
where there'd been irritating gunk just
like computers do biologists think that
our nose needs a reboot every once in a
while and it's kind of furry restart
button is made of all those cilia but it
turns out that not everybody's sneezes
actually reboot their nose in addition
to looking at healthy people cells this
same group of scientists took a peek at
the cells of people suffering from
sinusitis which causes inflamed sinuses
and general nasal discomfort runny nose
nasal congestion all that stuff they
discovered that when they puffed air
onto the tissue of the sinusitis
sufferers the cilia didn't beat fast
meaning that chronic sinusitis might
have to do with cilia that can't
properly reset post sneeze and that
knowledge might help researchers develop
treatments for it
I hope my cilia stays healthy so my nose
can stay clean with some occasional
cellular sweeping though all this talk
about your tents and nasal cells
wriggling is making my nose itch and
actually that's another odd thing our
bodies do [ __ ] even when we just think
about things
here's Michael again to explain why that
is
hitching just thinking about it is
making me kinda itch image can be caused
by all kinds of things the usual
culprits are things like bug bites
poison ivy or strands of hair brushing
against your skin but it's also brought
on by skin conditions like eczema or
psoriasis as well as seemingly unrelated
things like brain tumors diabetes and
chemotherapy with such a wide range of
causes the itch seems to be kind of
mysterious and it is but in the 2013
study published in the journal science
two researchers from the National
Institutes of Health discovered the
physiology of how itching works which
may eventually help chronic itches find
relief scientists used to think that an
itch was basically a low-level pain
signal meaning that one kind of nerve
cell detected both itching and pain but
the study found that itching is actually
linked to a set of special neurons that
produce a neuropeptide called NPPB the
scientists genetically engineered mice
said that they wouldn't produce NPPB
that exposed the mice to chemicals known
to produce itching these mice could
still feel their bodies heat pain and
touch but they didn't scratch no NPPB no
itch that's good news for people who
want to stop itching because the more we
understand about how itching works the
closer we can get to be able to control
it unfortunately it's not as simple as
just blocking this neuropeptide because
NPPB has another job too it's released
by the heart to regulate the amount of
sodium released by the kidneys which
helps control blood pressure but for
most people blocking itching wouldn't be
a good idea anyway the itch gets a bad
rap but it's a useful evolutionary
development scratching an itchy spot
could remove a pesky bug a dangerous
plant or some kind of other irritant
before they do damage to your body with
all this talk of itching you might be
starting to feel pretty itchy by now I
know I am just thinking about itches can
make you feel like spiders are crawling
all over you researchers gave a lecture
about itching to an unsuspecting crowd
to study their response and the audience
got to scratching with both a verbal and
visual itch cues and it's not just us
researchers have also studied the
contagious effect of itching on monkeys
and like a yawn being passed back and
forth the monkeys watched another
scratch and mirrored the behavior it
might be annoying but there's also an
evolutionary benefit to itching being
contagious one member of your group is
itchy that might mean they've been
exposed to a parasite or there's some
kind of irritant around which could mean
that you've been exposed to so it's
worth getting a head start on scratching
just in case
and now I'm feeling itchy all over
and since he mentioned yawning I'm
strangely tired too it's so weird that
we yawn just because we hear or see
someone else do it but why do we yawn in
the first place here's Hank with some
insights
people are always wondering about why do
people yawn and we do it every day
especially when we're in a boring
meeting or we didn't get enough sleep so
it may not surprise you that we don't
really understand all the reasons behind
why we yawn and it's not just humans
birds do it
Jaguars do it even fetuses in the womb
do it ah cetacean the act of yawning
happens with almost all vertebrates the
explanation you may be familiar with is
that a great big gaping yawn is the
brains way of ordering you to take a
deep breath supposedly it gets rid of
extra carbon dioxide and brings in more
oxygen problem with that is that there
is absolutely no truth that yawning
really affects your oxygen levels
instead recent studies show that yawning
is your brains natural air conditioning
system bringing cooler blood to chill
out your overheated overtired grey
matter your brain actually heats up as
it uses some 40 % of your body's
metabolic energy just like your laptop
gets warm when it's been playing video
games for hours body temperature also
rises and falls as part of your
circadian rhythm reaching its highest
point just before we fall asleep which
is why a series of yawns at 1:00 a.m. is
your body's Way of telling you to stop
going on reddit and just go to bed so
just like your computer has a fan to
cool things down a yawn does the same
thing to your brain allowing you to
continue processing information
effectively how's that work well since
you asked yawning has two parts first
stretching your jaws when you yawn
increases the rate of blood flow to your
skull second the inhalation sends the
gulp of air into your upper nasal and
oral cavities which have mucus membranes
covered with tons of blood vessels that
project up into the forebrain this is
the big part of the brain responsible
for receiving and processing sensory
information producing an understanding
language in controlling motor functions
many of the things involved in actually
being you so the cool refreshing air
entering your sinuses changes the
temperature of the blood that's now
hustling up to the brain making you more
alert and helping you walk and talk and
think more effectively don't believe us
scientists study the brain temperatures
of mice observing increased temperatures
before yawning and measuring a dip in
temperature afterward and a more simple
experiment on humans ask volunteers to
hold hot or cold packets to their heads
to see if changing the temperature of
their brain cases triggered yawning
turns out that the hot-headed
participants yawn 41% of the time all
those who chilled out yawn only 9% of
the time the next time you can't stop
yawning as you're falling asleep in a
sweltering class
room in the middle of the afternoon
remember that it's literally how your
brain keeps its cool
I guess my brain really needs to cool
down right now because I
I just can't seem to stop yawning so I'm
gonna head out but before I go I want to
say thank you to all of our patrons who
voted for this compilation topic we hope
you enjoyed the episode if you want to
support what we do here at scishow and
help us pick some future episode topics
you can learn more about becoming one of
our patrons at patreon.com slash scishow
and if you can't stop yawning either
well we have a whole episode on why
yawning is so contagious you can find it
over at our sister channel scishow site
a channel which I might add was also
picked by our patron community they're
just so awesome
[Music]
you