Final answer:
The diaphragm is a dome-shaped skeletal muscle that separates the thoracic cavity from the abdominal cavity and facilitates breathing by contracting and relaxing to change the volume of the lungs during inhalation and exhalation.
Step-by-step explanation:
The function of the diaphragm is to separate the thoracic and abdominal cavities and to aid in breathing. This domed-shaped skeletal muscle is located under the lungs and plays a crucial role during the breathing process. When the diaphragm contracts, the chest expands, and air flows in, which is the process of inhalation. Conversely, when the diaphragm relaxes, the chest contracts, which causes air to flow out, and this is exhalation. Additionally, the diaphragm works in cooperation with the abdominal muscles during activities such as defecating, urination, and childbirth, through a process known as the "Valsalva maneuver."