Final answer:
Contraction of the diaphragm during inspiration results in its downward movement, increasing the thoracic volume and leading to air inflow into the lungs.
Step-by-step explanation:
During inspiration, or inhalation, the external intercostal muscles and diaphragm play a critical role in expanding the thoracic cavity to allow air to enter the lungs. The contraction of the external intercostal muscles raises the rib cage, while the diaphragm contracts and moves downward. This downward movement increases the volume in the thoracic cavity, creating a negative pressure relative to the outside atmosphere, which causes air to flow into the lungs.
The external intercostal muscles, along with the diaphragm, work in tandem to facilitate breathing. When these muscles contract, the rib cage is lifted and expanded out and away from the lungs. The diaphragm, a dome-shaped muscle under the lungs, flattens and descends into the abdominal cavity, further increasing thoracic volume.
Upon relaxation during expiration, the diaphragm ascends back to its dome-shape, and the rib cage retracts, causing the pressure in the lungs to exceed atmospheric pressure, thus expelling air. This entire process is critical for the efficient exchange of oxygen and carbon dioxide within the body. The alternating contraction and relaxation of the diaphragm and intercostal muscles are essential for this life-sustaining act of breathing.
The final answer in two line explanation in 300 words for the movement of the diaphragm during inspiration is that the diaphragm contracts and moves downward, increasing thoracic cavity volume and facilitating the inflow of air into the lungs.