Final answer:
The primary muscles used for inspiration are the diaphragm and the external intercostal muscles, which expand the thoracic cavity and decrease pressure to allow air in. For deeper breaths, muscles like the scalenes and abdominal muscles assist in increasing lung volume.
Step-by-step explanation:
The muscles primarily used for inspiration during breathing are the diaphragm and the external intercostal muscles. The diaphragm is a dome-shaped muscle that contracts and flattens to increase the volume inside the pleural cavities, decreasing the pressure and allowing air to flow into the lungs. Contraction of the external intercostal muscles moves the ribs upward and outward, further expanding the thoracic cavity. For deeper or forced breathing, other muscles such as the scalenes in the neck and the accessory muscles of the abdomen contribute to increasing lung volume, facilitating the intake of more air. During relaxed breathing, the relaxation of these muscles causes air to be exhaled.
The muscles used for inspiration are the diaphragm and the external intercostal muscles. During inspiration, the diaphragm contracts and moves inferiorly, creating a larger thoracic cavity and more space for the lungs. The external intercostal muscles also contract, moving the ribs upward and outward, which expands the rib cage and increases the volume of the thoracic cavity. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure gradient that drives air into the lungs.