Normal Inspiration Process — NEET Biology

Which of the following statements regarding the mechanism of breathing are NOT correct? S1: During normal expiration, the relaxation of the diaphragm and inter-costal muscles reduces the thoracic volume, thereby increasing intra-pulmonary pressure above atmospheric pressure. S2: Forced expiration involves the active contraction of abdominal muscles and internal inter-costal muscles to forcefully reduce the thoracic volume further. S3: Inspiration is initiated by the contraction of external inter-costal muscles which lift the ribs and sternum, increasing thoracic volume in the antero-posterior axis. S4: The movement of air into and out of the lungs is primarily governed by creating a pressure gradient, with inspiration occurring when intra-pulmonary pressure is higher than atmospheric pressure. S5: Under normal conditions, expiration is a passive process because it does not involve the active contraction of muscles, relying instead on the elastic recoil of the lungs and relaxation of inspiratory muscles.