How do intercostal muscles contribute to lung expansion?

Intercostal muscles aid lung expansion by contracting and relaxing, altering the volume and pressure in the thoracic cavity.

The intercostal muscles are a group of muscles situated between the ribs. They play a crucial role in the mechanical aspect of breathing, particularly in the expansion and contraction of the lungs. There are two types of intercostal muscles: the external intercostal muscles and the internal intercostal muscles. Both types work together to facilitate the process of respiration.

The external intercostal muscles are primarily responsible for inspiration. When these muscles contract, they lift the rib cage upwards and outwards. This increases the volume of the thoracic cavity, which in turn decreases the pressure inside it. According to Boyle's law, the pressure of a gas is inversely proportional to its volume, given a constant temperature. Therefore, when the pressure in the thoracic cavity decreases, air rushes into the lungs to equalise the pressure, leading to lung expansion.

On the other hand, the internal intercostal muscles are involved in forced expiration. They pull the rib cage downwards and inwards when they contract, reducing the volume of the thoracic cavity and increasing the pressure. This forces air out of the lungs.

In addition to the intercostal muscles, the diaphragm, a large, dome-shaped muscle located at the base of the lungs, also plays a significant role in breathing. During inspiration, the diaphragm contracts and moves downwards, further increasing the volume of the thoracic cavity and aiding in lung expansion.

In summary, the intercostal muscles and the diaphragm work together in a coordinated manner to alter the volume and pressure in the thoracic cavity, facilitating the expansion and contraction of the lungs during respiration. This process is essential for the exchange of oxygen and carbon dioxide, which is vital for cellular respiration and the production of energy in the body.