Mechanics of breathing
Air moves from areas of high pressure to areas of low pressure. The greater the pressure difference, the faster the air flows. This means that in order to get air into the lungs (inspiration), the pressure needs to be lower inside the lungs than in the air we are breathing. The get air out (expiration), the presser needs to be higher in the lungs than in the air we are breathing.
Inspiration increases the volume of the thoracic cavity through contraction of the muscles surrounding the lungs. The diaphragm contracts and flattens while the external intercostals contract and pull the ribs up and out. This reduces the pressure in the lungs, drawing air in.
Expiration decreases the volume of the thoracic cavity. The diaphragm and external intercostals…