Question: what are the steps of inspiration?
Answer: inspiration 1. inspiratory muscles contract. ... 
inspiration 2. thoracic cavity volume increases.
inspiration 3. lungs are stretched. ... 
inspiration 4. intrapulmonary pressure drops.
inspiration 5. air flows into lungs down pressure gradient until pulmonary pressure is 0.
expiration 1. ... 
expiration 2. ... 
expiration 3.