Sneeze, cough, and hiccup - Biology, NEET Video Lecture

Let's say you have a
man and a birthday cake.
And he's really excited
to blow out the candles
so he can eat the cake.
So he's going to walk over.
Let me just cut and paste him.
There you go.
He's walked over.
And in the moment
before he walked over,
he was taking a
nice, deep breath.
And we call that inhaling.
So he was inhaling air.
And then as he was
next to the cake,
he was going to blow
out the candles.
So in the moment that he blew
out, that's called exhaling.
Now, we know that inhaling
requires a very powerful muscle
called the diaphragm.
That's one of the
most important muscles
I want you to
remember for inhaling.
And the other ones
are these muscles
that kind of are
between the ribs.
And they're called
the external--
external meaning closer to
the outside of the body--
external intercostal,
meaning between-- "inter"
just means "between"-- the ribs.
"Costal" refers to the ribs.
So external intercostal muscles.
These two groups, then--
the external intercostals
and the diaphragm
these two groups
are going to be very
helpful in inhaling air.
There are others
as well, but these
are the two you definitely
want to remember.
And for exhaling, there are
actually important muscles
as well.
We often think exhaling is
just kind of a passive process.
But if you're
blowing out candles
and you really want
to force air out,
there are actually
some muscles here.
And the two here that
I want you to remember
are the abdominal
muscles that really
help us to generate
a lot of pressure.
So abdominal muscles and then
these-- and the other ones
are called the internal
intercostal muscles.
Internal intercostal, so
"internal" comes up twice.
And these are actually
a little bit closer
to the inside of the body.
But they're also
between the ribs.
So these two muscle groups
are the most important ones
for exhaling.
And just to make sure you
get these two straight,
just look at these two words,
and you'll keep them separate.
So if things go as
planned, he's going
to be able to take
a nice deep breath,
inhale, and then
exhale a bunch of air
and basically wipe out these
candles and eat his cake.
So let's make a
little bit of space.
And I want you to just keep
in mind that this was all
happening in a
very voluntary way.
I mean, he wanted to blow
out those candles, right?
But what about some
involuntary things?
So let me draw up
some things that
are involuntary--
things that actually
seem to happen kind
of on their own,
where the brain is
just taking over
and you don't really
have to think about it.
And for the first example,
let me draw out the nose.
So this is the nose and a mouth.
And of course, we have, on
the inside, air coming in.
And we know the air
is going to meet up
between what's coming in
through the nose and the mouth.
And let's say that
you have some nerves.
And these nerves are right here.
And they're sensing some pollen
or some sort of irritant.
They're getting annoyed.
These nerves are going to
be called mechanoreceptors.
They're very sensitive,
and they can actually
pick up all sorts
of things like dust.
And so these
mechanoreceptors, if they
sense that there's
something there,
they're going to start sending
a signal up to the brain.
Now, here's the cool part.
That's the signal going in.
The signal coming
out of the brain
will basically do
a couple of things.
It'll lower the muscles here.
This is in the palate.
It'll lower the muscles there.
And it will raise the
muscle known as the tongue.
So the tongue will
come up a little bit.
And so now, these two are
going to work together
to basically close
off the mouth.
You can see how there's just
a tiny little space here
between the two where a little
air could go back through.
But most of the air is going
to have to go out this way.
So when you have a big
exhalation-- meaning air coming
back out if you're
exhaling-- you're
basically going to force air
to go out through the nose.
And now you might
be able to guess
where this is all
going to head to.
This is what we call
sneezing, right?
When you say, oh,
wow, I just sneezed,
this is what your body did.
It basically kind of forced
air through a forced exhalation
to go out through the
nose, and basically
wipe out anything
that was irritating
those mechanoreceptors.
So a sneeze is basically
just an exhalation,
or a powerful exhale,
through the nose.
And now you can
see how that works.
So pretty cool.
What's another example
of an involuntary thing?
Well, let's say that you
have your trachea here.
Your trachea branches.
And you have, of course,
some mechanoreceptors.
They're also here
lining the trachea.
And if they get
irritated again, they're
going to send a
signal-- you guessed it,
they're going to send
a signal to the brain.
So the brain is
going to know, hey,
something is
bothering my trachea.
The mechanoreceptors
have told me that.
Now, what's at the
top of this trachea?
The trachea is going to
have a little opening.
And that opening is going to
be where the vocal cords are,
right?
You've got your vocal
cords here on one side.
And on the other side,
there's a little opening
I left in black for
you to see where
air is going to go through.
This is where air
goes through usually,
and that's how we talk and sing,
right, through the vocal cords?
So these white things are my
vocal cords on both sides.
I've got two vocal cords, right?
And a little gap between them.
And what's going to happen is
that if the mechanoreceptors
are irritated, then
the brain is going
to basically do a couple things.
It's going to push air
out-- using, of course,
remember, those
abdominal muscles
and the internal
intercostal muscles.
It's going to push air out.
And it's going to
actually close off
these vocal cords, just
for a small moment.
It's just going to
close these off.
So what's going to
happen is that pressure
is going to build up.
You're going to get lots
and lots of pressure.
I'm going to put it with
an upward arrow and a P.
Lots of pressure in
the trachea, right,
as you build up
lots of pressure.
And then finally, a
split second later, it's
going to open the
vocal cords back up.
And air is going
to rush out, right?
So what we call that, when
that happens, is a cough.
We call that coughing.
So that's the word we use.
But really, what's happened?
We've had a very
powerful exhalation
using those muscles we
talked about, we've exhaled,
and then we've closed the vocal
cords, just temporarily, so
that you could build up
even more pressure, right?
Because if you're pushing
against something that's
closed, you can build up
pressure and then pop it open,
and then have almost, like, a
mini explosion in your trachea.
And we call that mini
explosion a cough.
A final example, let me actually
just sketch out very quickly,
your stomach.
Let's say your stomach has
got little mechanoreceptors,
maybe right here.
And these mechanoreceptors
are saying,
hey, you know, the
stomach is pretty full.
And so they're sending
messages up to the brain
to say, hey, brain,
we're very distended.
So a message is going
up to the brain.
So that's the message
coming into the brain.
So what could the brain do?
Well, just as
before-- let me just
draw out the trachea
kind of splitting off.
And in this case,
what's going to happen
is you have the vocal
cords, just as before.
Let me draw them in
like this, right?
Little vocal cords.
And these vocal cords are
initially going to be open.
And air is coming through.
And this is, of
course, inhalation.
We're inhaling right now.
Let me write that out, inhaling.
So inhaling air using the
muscles of inhalation-- we
said primarily the diaphragm
and the external intercostal
muscles.
And then, just as before,
the vocal cords close.
So all of a sudden, now you
have closed vocal cords.
So what's going to happen if
that vocal cord closes off--
or the vocal cords close off?
Well, the air is literally
going to not be able to come in.
It can't come in anymore.
So you have this
kind of bouncing off,
where the air
literally bounces off
of these closed vocal cords.
It can't go anywhere.
And when you have air rushing
in and then bouncing off
of the closed vocal cords,
you know what we call that?
We call that a hiccup.
We call that a hiccup.
So it's kind of
interesting how this
is, in some ways, kind of the
opposite of a cough, right?
In the cough, you
had air that was
being exhaled in the
closed vocal cords.
And then here, you have
air that's being inhaled,
and you have the
closed vocal cords.
And of course, when I say
the closed vocal cords,
it's very, very instantaneous.
It's just for a quick moment.
And that's what
causes the big change.
Why we hiccup is still
a bit of a mystery,
but at least now you have
a little bit of insight
into how that actually works.