2.7. Overview of the Diaphragm
The Muscular Diaphragm
The diaphragm is a muscular sheet with a tendinous centre (called the ‘central tendon of the diaphragm’). There are no bones in the diaphragm! The function of the diaphragm is to contract to allow inspiration to occur. When the diaphragm relaxes, expiration occurs. Basically, the diaphragm facilitates ventilation of the lungs. It is the most important muscle when you are breathing normally and quietly - it is even more important than the intercostal muscles. The diaphragm, which has two 'domes' when it is relaxed, flattens considerably during inspiration, and then returns to its two-domed shape during expiration.
Note that the domes are not symmetrical – when the diaphragm is relaxed and the two domes can be seen, the right dome lies slightly higher than the left dome. This is because the diaphragm is making a little space for the liver on this side. The liver is a huge structure and is largely tucked up under the ribcage. Confirm the heights of the diaphragm during respiration in the accompanying diagram.