Complete NPTE Practice Exam 2025 – Full Prep Guide

The diaphragm is the primary muscle responsible for inspiration, playing a crucial role in the respiratory process. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and decreasing the pressure within it. This pressure change allows air to flow into the lungs. The diaphragm's efficiency in this function is vital for effective breathing, especially during rest and physical activity.

Other muscles, such as the internal intercostals and scalenes, assist in the respiratory process but are not the main drivers of inspiration. The internal intercostals primarily aid in expiration, especially during forceful exhalation, while the scalenes assist in elevating the first two ribs to facilitate deeper inhalation under specific conditions. The transversus abdominis is more involved in forced expiration and core stability than in inspiration. Thus, the diaphragm stands out as the key muscle facilitating the intake of air during respiration.