Final answer:
The diaphragm is a dome-shaped skeletal muscle that separates the thoracic and abdominal cavities and is the primary muscle for breathing. It is primarily innervated by the phrenic nerve and is responsible for changing the pressure and volume in the chest cavity during respiration.
Step-by-step explanation:
The diaphragm is a sheet of skeletal muscle that plays a critical role in the process of breathing. It separates the thoracic and abdominal cavities and is normally dome-shaped when at rest. The diaphragm is the primary muscle of breathing and is responsible for the expansion of the thoracic cavity during inhalation, which leads to air being drawn into the lungs. The contraction of the diaphragm flattens the muscle, creating more space in the chest cavity and thus reducing the pressure inside, leading to the inflow of air.
The phrenic nerve provides the primary innervation to the diaphragm. When the diaphragm contracts, air flows into the lungs; as it relaxes, the chest cavity contracts, and air flows out. This muscle is also involved in the Valsalva manoeuvre, which occurs during activities such as defecating, urination, and childbirth in cooperation with the abdominal muscles.