The diaphragm is the muscle located under the ribs. Diaphragm is the structure tat helps separate the abdominal and thoracic cavity that is comprised of ribs ,heart and lungs.Diaphragm is a very important organ of the human body because of the fact that it performs on various tasks which are important to keep something living.
During the process of breathing,the diaphragm contracts to add volume to the thoracic cavity, which enables the lungs to make room for more air. This phenomenon occurs in two  diverse varieties of respiration.The first is known as abdominal respiration, where the thoracic cavity stretches downwards. The second kind of respiration is referred to as thoracic respiration and enables the thoracic cavity to extend upwards.  

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The diaphragm expands the chest cavity allowing us to breathe in