Which muscles are primarily responsible for the process of breathing?

The muscles that are primarily responsible for the process of breathing are the intercostal muscles and the diaphragm. The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity. When it contracts, it flattens and increases the volume of the thoracic cavity, creating a negative pressure that pulls air into the lungs. The intercostal muscles, situated between the ribs, assist by elevating the rib cage, which further expands the thoracic cavity and facilitates inhalation.

In combination, these muscles enable the efficient exchange of oxygen and carbon dioxide in the lungs during the respiratory cycle. Respiration can be categorized as either active or passive. During active inhalation, both the diaphragm and the intercostal muscles contract, while in the passive exhalation phase at rest, the muscles relax, allowing the natural elastic recoil of the lung tissue and thoracic wall to push air out.

The other answer options involve structures or types of muscles that do not primarily facilitate breathing. Smooth and cardiac muscles are involuntary muscles that perform functions in systems such as digestion and circulation, while abdominal and skeletal muscles can assist in forcing air out during vigorous activities but are not the primary muscles involved in the normal respiratory process. Lastly, veins and arteries are blood