How Breathing Is Controlled

You can control your breathing almost anytime you want, whether it's to blow up a balloon or to play a musical instrument. But this doesn't mean that breathing is purely voluntary. If you hold your breath for a minute or so, you'll see what happens. Your chest begins to feel tight, your throat begins to burn, and the muscles in your mouth and throat struggle to keep from breathing. Eventually your body takes over. It “forces” you to breathe!

Breathing is such an important function that your nervous system will not let you have complete control over it. The part of the brain that controls breathing is the medulla oblongata. Autonomic nerves from the medulla oblongata to the diaphragm and chest muscles produce the cycles of contraction that bring air into the lungs. How does the medulla oblongata “know” when it's time to breathe? Cells in its breathing center monitor the amount of carbon dioxide in the blood. As the carbon dioxide level rises, nerve impulses from the breathing center cause the diaphragm to contract, bringing air into the lungs. The higher the carbon dioxide level, the stronger the impulses. If the carbon dioxide level reaches a critical point, the impulses become so powerful that you cannot keep from breathing.

That the breathing center responds primarily to carbon dioxide can have dangerous consequences. Consider a plane flying at high altitude. Although the amount of oxygen in the air decreases as the altitude increases, the passengers do not need oxygen masks because the cabin is pressurized. Oxygen is available for use in an emergency, but the passengers often have to be told to begin breathing the oxygen. Although their bodies may be starving for oxygen, they have no more carbon dioxide in their blood than usual, so the breathing center does not sense a problem.

How does your body respond to increases in carbon dioxide? Materials  seltzer tablet, plastic cup Procedure  Formulating Hypotheses Carbon dioxide is a waste material synthesized during the cellular process of respiration. Write a hypothesis about how your breathing will be affected if the level of carbon dioxide increases. Place approximately 100 mL of water in the cup and add a seltzer tablet. The bubbles in the water are carbon dioxide. Bring the cup up to your face and inhale deeply. Analyze and Conclude  Observing Describe what happened when you inhaled the carbon dioxide. Drawing Conclusions Did your results support your hypothesis or not? Explain your answer. Inferring Why is it important for your body to respond to the stimulus of increased carbon dioxide?