Inspiration occurs when there is a negative pressure in the lungs with respect to atmospheric pressure. This negative pressure is achieved when

Answer: ASolution: Because of the pressure gradient between the lungs and the atmosphere, the air moves into and out of the lungs. Inspiration occurs if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure i.e. there is a negative pressure in the lungs with respect to atmospheric pressure.