What is the primary muscle involved in inspiration?

The diaphragm is the primary muscle involved in inspiration. When the diaphragm contracts, it flattens and moves downward, increasing the volume of the thoracic cavity. This change in volume creates a negative pressure that draws air into the lungs. This process is essential for passive and active inhalation.

While other muscles can assist in the process of inspiration, the diaphragm is the most significant and effective muscle for this function. The intercostals, for example, play a supportive role by helping to elevate the ribcage, but they do not initiate inspiration. Similarly, the abdominal muscles are primarily involved in forced expiration rather than inspiration. The scalenes can aid in lifting the upper ribs during deep or labored breathing, but they are not the primary initiators of the inspiration process. Thus, the diaphragm’s main role in altering thoracic volume makes it the correct choice in identifying the primary muscle involved in inspiration.