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- [Presenter] Even though we're dealing

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with the respiratory system,

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we have to talk about the nervous system,

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because the nervous system is

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what will control your respiration rate.

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It'll control how many
breaths you take per minute.

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We have this respiratory center

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in the medulla oblongata,
that's basically the brain stem.

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This helps to establish
your breathing pattern.

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Do you breathe 12 times a minute,

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15 times a minute, 18 times a minute?

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It sets how many times
you breathe in a minute.

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Typically about every five seconds or so,

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the neurons are stimulated.

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This causes your intercostal muscles

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and the diaphragms to be activated.

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Usually when you're breathing calmly,

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just regular breathing,

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it's traditionally just
the diaphragm, the muscle

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at the bottom of your
lungs, that's working.

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The intercostal muscles,
more often than not,

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are simply there for deep
breaths or forced exhalation.

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Why do we breathe?

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We breathe to bring in oxygen

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and get rid of carbon dioxide, CO2.

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One thing your body must do is monitor

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the carbon dioxide levels

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to see if you have too much or too little.

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If your carbon dioxide--that's
the up arrow P CO2,

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If the partial pressure of carbon dioxide

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in your blood goes up,

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it causes too many hydrogen ions, H+,

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in your cerebrospinal fluid.

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Cerebrospinal fluid, that's the stuff

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that's around the brain.

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It's around the spinal cord.

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If that happens, the brain
and spinal cord will realize

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and say, "Hey, we've got a problem here.

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"Let's increase our respiratory rates."

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By breathing faster, it means
you'll have more opportunity

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to get rid of carbon dioxide.

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So the increased respiratory rate helps

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to get rid of an increase
in carbon dioxide.

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This really is the main, or primary,

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regulation of respiration.

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You're not necessarily looking for oxygen.

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You're looking for carbon dioxide,

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because the two are linked, true.

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Usually if you have more carbon dioxide,

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you have less oxygen.

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If you have more oxygen, you
have less carbon dioxide.

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But it's this increase in carbon dioxide

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that changes the hydrogen ion level.

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It's that hydrogen ion level
that really makes a difference.

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Just because carbon dioxide is the main

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controlling factor for respiration

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doesn't mean you ignore oxygen.

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You still monitor your partial
pressure of oxygen, P O2.

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In your aorta--

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that's the major blood
vessel coming off your heart,

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and your carotid bodies--

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those are the major blood
vessels running up to your brain,

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you're gonna monitor your oxygen levels.

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If your oxygen levels fall
too far down, or too low,

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those bodies are automatically activated.

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By activating, it'll increase
your respiratory rate,

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but also increase the depth of breathing.

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What's happening here now is,

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just like carbon dioxide,
you're breathing faster,

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but you're also breathing deeper,

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bringing more air into the lungs.

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The more air you breathe in,

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the better chance and higher
rates of oxygen diffusion,

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getting oxygen into your body.

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The rates and depth of normal breathing,

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what you're doing right now,

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is determined by the fact that you need

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to get rid of carbon dioxide.

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It's not necessarily
because you need the O2,

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you need the oxygen,

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it's more because you're trying to get rid

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of the carbon dioxide.

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When you get rid of the carbon dioxide,

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your body automatically picks up more O2.

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So really the main driving
factor behind normal breathing

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is the fact that your body
must get rid of carbon dioxide.

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Can we modify our breathing?

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Sure, we have some ability

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to consciously control our breathing.

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For instance, if I said right now,

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"Increase your respiratory rate,"

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you could start to breathe faster.

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In out, in out, in out.

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But if I said, "Slow it down,"

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you could slow it down a little bit.

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Breathe a deep breath and slowly

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and slowly exhale out.

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But you can only maintain this
for a certain period of time.

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Speaking, singing, are also
modifications of breathing.

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When you're singing a song,

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do you stop right in the middle of a word

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to take a breath usually?

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Or you're speaking.

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Are you also gonna be saying a word

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and stop halfway through a word,

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take a breath and continue on?

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If I read that first sentence,

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"Conscious control resides
in the cerebral cortex,"

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I didn't even take a breath in there.

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But if I try doing this,

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tell me if this sounds normal:

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"Conscious con--(loud breath)

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"trol resides in the (loud breath)

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"cerebral cor--(loud breath) tex."

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No, because it doesn't make sense.

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You're breaking apart the word,

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because you're not
controlling the breathing

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at a proper point.

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What ends up happening now is

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to read, to speak, to
sing, any vocalization

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you want to control your breathing

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to make sure it sounds and makes sense.

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The whole idea of holding
your breath temporarily,

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that varies from person to person.

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Someone temporarily holding their breath

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might be for only 20 or 30 seconds.

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No problem.

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Someone else that's a
little more used to it,

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maybe they're a swimmer,

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might be able to hold their breath

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for three, four, five minutes.

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It all depends on lung capacity

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and your ability to
regulate your body activity.

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But eventually your body's gonna say,

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"Uh-uh, I'm done."

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Your body will actually override

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your ability to hold your breath

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and say, "Start breathing."

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Even if you try to hold your breath,

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you'll hold it, hold it, hold it,

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you might feel like it starts to hurt,

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you might start to see a
little black in the eyes.

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But eventually your body
automatically starts to breathe.

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If you're stubborn,

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you might even make
yourself pass out first.

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But the minute you pass out,

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your body takes over
and you start breathing.

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Don't go trying this please,

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(laughs) but the idea is your brain

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is going to override
your conscious thoughts.

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The brain's looking out for your body.

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It'll make sure you take
a breath at some point.

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So here we see the brain

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and how it's connected
down into the lungs.

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First off, the respiratory cells
near the respiratory center

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respond to change in cerebrospinal fluid.

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We're down in the brain
stem, medulla oblongata.

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If this happens because of an
increase in carbon dioxide,

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then receptor cells in the
carotid aorta also respond.

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But they're responding
to a decrease in oxygen.

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Even the higher centers in the cortex,

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your conscious control,

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you can consciously increase
or decrease respiration.

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That means there are three different ways

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your body's monitoring
and can control breathing.