Mechanism Of Respiratory System Respiratory centre is in Medulla Oblongeta. Mechanism of breathing involves Two Phases. (A) Inspiration (B) Expiration Inspiration: Intercostal and phrenic muscles of diaphragm contract to increase thoracic cavity, therefore outside rushes inside. Expiration: Intercostal & phrenic relex muscles. Due to decrease of thoracic cavity air … [Read more...] about Mechanism Of Respiratory System