Final answer:
Movements of the thorax are most prominent in the upright position due to the natural position of respiratory muscles and gravitational effects. The external intercostal muscles' contraction results in the expansion of the rib cage. The cervical region of the vertebral column has the greatest range of motion for rotation.
Step-by-step explanation:
Movements of the thorax become more prominent in the upright position. When a person is standing upright, the motions involved in breathing are easier to observe due to a combination of gravitational effects and the natural position of the respiratory muscles. This position is contrasted with supine (lying on the back) or prone (lying on the stomach), where movements may be less observable due to the body's position against a flat surface, potentially restricting the observable range of motion of the thorax.
Contraction of External Intercostal Muscles
In relation to the thorax and respiratory movements, contraction of the external intercostal muscles pulls the ribs up and outward, expanding the rib cage and allowing for inhalation. This movement contrasts with the rib cage being compressed, which would occur during exhalation. Therefore, the correct answer is that the diaphragm moves downward and the rib cage expands.
Greatest Range of Motion in the Vertebral Column
The region of the vertebral column that has the greatest range of motion for rotation is the cervical region. The intricate structure and flexibility of the cervical vertebrae permit a significant degree of rotation compared to the thoracic, lumbar, or sacral regions.