Question

During inspiration in man,

• A. The external intercostal muscles relax
• B. Due to contraction of external intercostal muscles and flattening of diaphragm, the volume of thoracic cavity increases
• C. Due to contraction of external intercostal muscles and flattening of diaphragm, the volume of thoracic cavity decreases
• D. The abdominal muscles contract

Answer 1

Answer: (B)

Due to contraction of external intercostal muscles and flattening of diaphragm, the volume of thoracic cavity increases

The thoracic diaphragm consists of the peripheral muscle and central tendon. The peripheral muscle is made up of many radial muscle fibers that originate on the ribs, sternum, and spine and converge on the central tendon. On the basis of origin, the peripheral muscular part is separated into sternal, costal and lumbar. When we breathe, the diaphragm is drawn downward until it is flat. the thoracic cavity becomes deeper and larger, making more air space. when air is drawn into the lungs, the muscles in the diaphragm contract pulling the central tendon down. This process enlarges the thoracic cavity, and air then passes into the lungs to fill the larger space.