How are the ribs pulled upwards and outward when a person inhales?

During inhalation, several muscles work together to expand the chest cavity and draw air into the lungs. The primary muscle responsible for pulling the ribs upwards and outwards is the diaphragm, which is a large, dome-shaped muscle located at the bottom of the rib cage.

Here's how the diaphragm contracts to facilitate inhalation:

1. Contraction of the Diaphragm: When a person inhales, the diaphragm contracts and flattens. This movement increases the vertical space within the chest cavity.

2. Transmission of Force: As the diaphragm contracts, it pulls on the costal margin (the lower edges of the rib cage) and the costal cartilages (which connect the ribs to the sternum). This force is transmitted to the ribs, pulling them upwards and outwards.

3. Intercostal Muscles: In addition to the diaphragm, certain intercostal muscles also contribute to pulling the ribs upwards during inhalation. The external intercostal muscles, which lie between the ribs, also contract during inhalation, further assisting in expanding the thoracic cavity.

When the ribs are pulled upwards and outwards, the volume of the chest cavity increases. This creates a lower pressure within the lungs compared to the atmospheric pressure outside. As a result, air rushes into the lungs, causing inflation.

The act of exhalation is largely a passive process, relying on the natural elasticity of the lungs and the relaxation of the diaphragm and intercostal muscles to force air out of the lungs.