So in this video what I wanted to focus on
is one particular area of the brain-- actually, two areas
I'm going to sketch out, not just one.
I'm going to show you how I think that these two areas can
be kind of united in a way.
So, these two areas, where I'm sketching out
these little green circles, are going
to be responsible for breathing-- how fast you
breathe, how deep you breathe.
And there are lots of little neurons in these two areas.
And these neurons are going to be communicating.
Let's say this neuron sends a little axon on down here,
maybe this guy sends an axon up here.
They're going to be communicating information
among themselves and between themselves
to kind of make sure they're working in a coordinated way
so that the breathing that you do
is the way that it should be, you know,
how fast it should be, given a particular situation.
So the way I think of it is kind of uniting these two areas.
In fact, sometimes it's subdivided even further.
I just put it all together and say this part of the brain
that I'm just sketching out in green,
this area then, is our respiratory center.
This is going to be responsible for all
of the important activities of breathing.
So let me just write that out here.
So our respiratory center is going
to gather information from different places.
And then it's going to have to make a decision
and execute based on all the information it receives.
So one key piece of information is
going to come from cells right here, neighborhood cells.
And these cells are called the central chemoreceptors.
The reason I'm calling them central
is because they're also part of the brain, right?
They're right in the same neighborhood,
and so these central chemoreceptors
don't have to go too far to communicate their information.
And specifically they're going to gather information
on things like carbon dioxide levels and pH levels.
One thing they don't do is oxygen levels.
So that's these guys right here.
So if you have central chemoreceptors
you also probably can expect that there
would be some peripheral chemoreceptors,
and these ones are also very important.
And they exist outside of the brain,
so they're going to be actually sending their information
along through neurons that are going
to extend all the way into the brain.
So for example, you might have two key groups.
One is called the aortic body and the other
is called the carotid body.
Aortic body and the carotid body.
They're coming from different locations
and are actually going to use different nerves
to get into the brain.
So the carotid body, for example,
is going to extend out this way through a neuron.
And that's going to be through a nerve called the-- right here--
called the glossopharyngeal nerve.
This is cranial nerve number nine, also
called the glossopharyngeal nerve.
So this is one of the key peripheral chemoreceptors.
You've also got some nerves or neurons projecting
from the aortic body going through the vagus nerve.
So this is our vagus nerve, or cranial nerve number 10.
It goes by two different names.
These peripheral chemoreceptors are
going to detect things like oxygen--
in fact, that's probably one of the most important things they
detect-- as well as carbon dioxide and pH.
So that's information coming to the respiratory center
from our peripheral and central chemoreceptors then
is mostly about chemicals.
In addition, there's another whole group
of receptors called mechanoreceptors.
And these ones are actually going
to be sending information about pressure.
Now you may be thinking, well, wait a second.
I thought baroreceptors told us about pressure.
And it turns out, baroreceptors are one type of mechanoreceptor
that's found inside of the blood vessels.
So there are many other types and many other locations.
And so the bigger, more general term would be mechanoreceptor.
You can find them in places like the nose,
you can find them in the lungs, in the GI tract,
so lots of different locations for these mechanoreceptors.
And they're all sending their own projection
over to the respirator center.
And in fact, the lungs and the GI tract
are going to hitch a ride in this vagus nerve
and the nose mechanoreceptors they're
going to travel through another nerve that's
called the trigeminal nerve or cranial nerve number five.
So these are the routes that these receptors
are going to take to get to that respiratory center.
But how do these work exactly, these mechanoreceptors?
Let's take an example.
Let's say you're walking and you inhale some pollen.
Well, that's going to trigger one of these mechanoreceptors
in your nose and it's going to want
to relay that information over to your respiratory center
so you're going to get a little nerve
impulse through that cranial nerve number five.
Similarly in your lungs, let's say
you actually inhale some cigarette smoke.
And let's say the lungs don't like that.
And then the mechanoreceptor feels that little particle.
It's going to trigger cranial nerve
number 10, the vagus nerve.
Similarly, you have these stretch receptors
that are in the lungs.
And these are actually kind of interesting
because what they're doing is they're saying,
hey, you know these lungs are starting to get really, really
full, really distended, and so they
want to let the respiratory center know that maybe it's
time to exhale.
And similarly, in the GI tract you can imagine,
let's say a baby is taking milk and the stomach
is getting really distended, you might also
imagine that that information would go back
to the respiratory center as well, in this case
through cranial nerve number 10.
So we have information about pressure or stretch,
we also have information about chemicals coming in.
But what about information on things like,
I don't know, things like anxiety for instance, or fear.
Let's say someone is having these emotions.
Their breathing pattern may change.
Maybe they're in pain.
So these kinds of things are actually
coming from the hypothalamus.
So this is another region of the brain that's
sending information down to the respiratory center
and helping to affect how we breathe.
And finally, this is probably the largest part
of our picture, this is our cerebrum.
And the cerebrum is responsible for all the voluntary stuff
that we do, things like singing, where
you've got to control your breath.
Or maybe you're playing a musical instrument,
or maybe you're yelling or screaming.
Let's put yelling down here.
Anything like that, you're going to want to control your breath.
And so that's all voluntary control.
So this is our voluntary control.
And it's good that actually we have this mechanism
so we can-- if we want to-- we can change our breathing
But it's also great that our respiratory center
can work on its own.
Can you imagine if you had to always think
about taking a breath?
You couldn't do anything else, right?
You couldn't sleep, you couldn't eat.
You would always just be thinking
about taking a breath so that you wouldn't
miss the next breath and subsequently run out of air.
So this is all the information coming
into our respiratory center.
Let me just scoot this over and actually show you now
what our brain can do with that information to actually make
sure that we're breathing comfortably.
This is our spinal column.
And I'm actually just going to label out
the motor nerves and some of the muscle groups.
So we've got motor nerves and muscle groups.
And there are four key muscle groups
that are going to be controlled by our respiratory center.
And we're going to go through them one by one.
So the first one, and the one that people usually always talk
about or think about, is this one right here.
This is going to be C3, C4, and C5.
So C3 through C5, and the muscle is the diaphragm.
This is the giant muscle that kind of sits right
below our lungs and when it contracts
you take in a nice deep breath.
But it doesn't work alone.
We've got other muscles involved as well.
So I'm actually going to sketch out
what these other muscle groups are.
The first one is T1 through T11.
All these levels are going to send off a little nerve.
And each nerve will go through a different intercostal muscle.
So intercostal muscles are-- these
are the muscles that kind of go between the ribs--
these are going to help expand or pull out your ribs, right?
So these are important for breathing as well.
A little bit lower then, you also
have these abdominal muscles.
Abdominal muscles here are going to be T6 through L1.
These are the levels where the little nerve
fibers come out and are going to help innervate or help
these muscles, abdominal muscles, contract.
So this is a third group of muscles
and they're controlled by these spinal levels.
And the final group would be this group up here.
So this is actually C1 through C3.
And these would be the accessory muscles.
Accessory muscles are the ones-- usually
I think of them as the ones around your neck area.
And they're going to also kind of help pull out the rib cage
and expand the lungs.
So there you have it.
You have information coming in, that's
the stuff that we started talking
about, from all the different locations,
around chemicals, information about pressure,
and your emotional status, and what
you're thinking about doing involuntarily.
All that information is going to come in
and then the respiratory center has
to decide how to kind of balance all that information.
And on the way out it's going to be
able to execute by controlling all these different muscle
groups and sending information down the motor nerves
that we just listed to these four big groups of muscles.