Dr. Jack Feldman

And it's like pulling on a spring.

You pull down a spring, and you let go, and it relaxes.

Where does that activity originate?

The region in the brainstem.

That's, once again, this region sort of above the spinal cord, which was critical for generating this rhythm.

It's called the pre-Butzinger complex.

This small site, which contains, in humans, a few thousand neurons, is located on either side.

and works in tandem, and every breath begins with neurons in this region beginning to be active, and those neurons then connect ultimately to these motor neurons going to the diaphragm and to the external intercostals, causing them to be active and causing this inspiratory effort.

When the neurons in the pre-button complex finish their burst of activity,

then inspiration stops and then you begin to exhale because of this passive recall of the lung and rib cage.

I don't think we fully have the answer to that.

Clearly, there are differences between nasal and mouth breathing.

At rest, the tendency is to do nasal breathing because the air flows that are necessary for normal breathing is easily managed by passing through the nasal cavities.

However, when your ventilation needs to increase, like during exercise, you need to move more air

you do that through your mouth because the airways are much larger then, and therefore you can move much more air.

But at the level of the intercostals and the diaphragm, their contraction is almost agnostic to whether or not the nose and mouth are open.

So when we discovered the pre-butzinger, we thought that it was the primary source of all rhythmic respiratory movements, both inspiration and expiration.

And then in a series of experiments, we discovered that there was a second oscillator, and that oscillator is involved in generating what we call active expiration.

That is this active... Like if I go shh.

Yeah, or when you begin to exercise, you have to go...