Explain the process of inspiration under normal conditions.
Inspiration is the process by which atmospheric air is drawn into the lungs. It occurs due to the creation of a pressure gradient between the lungs and the atmosphere.
For inspiration to occur, the pressure within the lungs (intra-pulmonary pressure) must be less than the atmospheric pressure. This creates a negative pressure in the lungs with respect to atmospheric pressure.
The process is initiated by the contraction of the diaphragm, which increases the volume of the thoracic chamber in the antero-posterior axis. Simultaneously, the contraction of external inter-costal muscles lifts up the ribs and the sternum, causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.
The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure.
This pressure gradient forces the air from outside to move into the lungs, completing the process of inspiration. The diaphragm and specialised muscles help in generation of such pressure gradients.
Explanation
This answer covers all key aspects of inspiration from the NCERT textbook: (1) definition of inspiration, (2) the pressure gradient requirement, (3) role of diaphragm contraction, (4) role of external inter-costal muscles, and (5) how increased pulmonary volume leads to decreased intra-pulmonary pressure causing air to enter lungs. The answer follows the logical sequence presented in the textbook and uses appropriate biological terminology.