The part of the human body that tightens and moves down to create lower
air pressure in the lungs than in the outside environment, allowing
air to move into the lungs. This part then relaxes and moves back up, generating higher
air pressure in the lungs than the outside environment, forcing carbon dioxide out of the lungs. This part also separates the chest cavity (cardiovasuclar and respiratory) from the abdominal cavity (digestive system), which is why your chest expands as you breathe. Also that fancy part of an air
horn that rapidly vibrates in response to
air movement, generating that screeching sound.
(From
Business Insider) "When you take a breath in, your diaphragm tightens and is pulled down to
allow your lungs to expand. When you exhale, your diaphragm relaxes and is pushed back up to expel the
air from your lungs."