The Control of Breathing Mechanisms in Humans

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The Control of Breathing Mechanisms in Humans

All living things require energy. This energy is obtained by breaking down sugars and other substances through the process of respiration. As a consequence of respiration, gaseous exchange takes place. Breathing is essential to humans in order to provide the oxygen required for aerobic respiration and also to get rid of carbon dioxide produced as a waste product of respiration. The breathing mechanism in humans is more complex than small animals because of the need for an intricate system that delivers all over the body. We know that air needs to be taken in and out of the body. These processes, called inspiration and expiration, take place due to pressure gradients created in the lungs. These pressure changes are brought about by changes in the volume of the thorax. The volume of the thorax in turn changes as a result of movements of the ribs and diaphragm caused by muscle contractions.

This whole ventilation cycle occurs in a rhythmic fashion. However, unlike the cardiac muscles which have the property of intrinsic rhythmicity, the muscles controlling breathing do not have inherent rhythmicity, but are instead remotely controlled by motorneurones in the spinal cord. More specifically, the major muscles in breathing, the intercostal muscles, are controlled by the intercoastal nerves from the thoracic segments of the spinal cord, and the diaphragm whose motorneurones are in the phrenic nerve from the mid-cervical region of the spinal cord. Although these motorneurones control the muscles used for breathing, they are not the root control centre of the whole operation. The nerves producing breathing are spread through much of the spinal cord so there must be something which co-ordinates them.
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If the spinal cord is cut in the lower cervical region, the intercoastal muscles are paralysed but breathing continues as normal due to the diaphragm. If the spinal cord is cut above the phrenic nerve, all respiratory muscles will be paralysed. This shows that there must be control from the brain. When a cut is made through the brain stem so that the medulla oblongata is connected to the spinal cord but separated from the rest of the brain, breathing will continue regularly, so the cells controlling the breathing are in the medulla and are called the respiratory ...

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