Which muscles contract to cause air to pass into the lungs through the trachea?

The muscles are external intercostal muscles, diapraghm and the abdomen muscles contract to allow air to pass into the lungs through the trachea. These muscle contractions will result in an added volume of the thorax which in return will cause in a pressure drop in the thorax. These contractions are essential in inhalation and exhalation.

They use the si unit, or metric system its all the same thing