As the domelike diaphragm contracts, it moves _ ?
a. upward
b. medially
c. laterally
d. downward
The correct answer and explanation is:
The correct answer is d. downward.
Explanation:
The diaphragm is a dome-shaped muscle that separates the thoracic cavity (which contains the lungs and heart) from the abdominal cavity. It plays a critical role in the process of breathing. When the diaphragm contracts, it flattens and moves downward, increasing the volume of the thoracic cavity. This movement creates a pressure difference between the inside of the lungs and the outside environment, causing air to flow into the lungs.
The contraction of the diaphragm is stimulated by signals from the brain through the phrenic nerve. As the diaphragm contracts, the central part of the muscle moves downward, and the ribcage expands as well, allowing the lungs to fill with air. This process is part of the mechanism of inhalation.
When the diaphragm relaxes, it moves upward into its dome shape, which helps to expel air from the lungs during exhalation. This upward movement decreases the volume of the thoracic cavity, increasing the pressure inside the lungs and forcing air out.
So, the key point is that the diaphragm moves downward during contraction to create space for the lungs to expand as they fill with air.