Breath Series - Part 1

A single breath. It's the first thing we do as human beings and, truly, the very last. It welcomes us in and ushers us out. It sustains us through everything in between. It is a marvelous, intricate, beautiful bodily process that deserves a closer examination.

For this first installment in my "Breath Series" I'll start at the beginning...

Q: How do we breathe?

A: It's a commonly believed notion that the chest expands simply because air has moved into the lungs and it pushes the chest out. In truth, it's actually just the opposite. The chest expands in order to make room for the oxygen. It actually has a lot to do with air pressure. Based on Boyle's Law, in order to lower the air pressure in the lungs, the volume must first be increased. So, the chest expands (which means the volume has increased), the lung pressure drops, air is then sucked into the lungs as a natural means to balance the lung pressure and the atmospheric pressure--or in other words, inhalation happens! Conversely, to move air out of our lungs, the chest falls (which decreases the overall volume), this causes the lung pressure to increase, and, what do you get? Exhalation! Air naturally flows out of the lungs and back into the wide world, at least until the lung pressure equals the atmospheric pressure.

Now you might be wondering, "Wait, what causes the chest to expand in the first place?" Enter diaphragm. The diaphragm is the lovely dome-shaped muscle/tendon that is actually the main player in the respiratory system. Because of its contracting up and down, respiration is possible (with some help from the intercostal and abdominal muscles-give credit where credit is due). Whenever it contracts, flattening down, then the chest expands, the lung pressure drops...inhalation. Conversely, when it relaxes, returning back into its dome shape, it compresses the thoracic cavity, causing the chest to fall, the lung pressure to increase...exhalation.

Simple...right?

This begs the same question: "What causes the diaphragm to contract in the first place?" This leads us to the autonomic nervous system which connects the brain stem to specific bodily processes. In this case, the phrenic nerve connects from the C3, C4 and C5 vertebrae of the spine down to the diaphragm. Breathing, most of the time, is automatic and we do it subconsciously under the direction of the respiratory center at the base of the brain--and thank goodness for that! Can you imagine the burden life would be if we had to consciously take every breath? We wouldn't be able to do anything else, not even sleep, for fear of forgetting to take the next one. But thankfully this respiratory center is working around the clock, gathering endless amounts of data from its many different nerve channels, then processes all of that data, then decides how to proceed. Should it signal the diaphragm to contract? Should it signal it to relax?

And so it is here that the breath, and all of oxygen-breathing life, begins. A nerve process in the brain sends a signal to the diaphragm, the diaphragm contracts, the thoracic cavity expands, the pressure lowers, a vacuum is created, air flows into the lungs, and a baby take its first breath...all of this in a matter of seconds.

So...what causes the nervous system to do its thing in the first place? No, really, can someone explain it to me?

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