Our lungs do not have muscles, and yet air moves in and out of them. Explain how this occurs.

The movement of air in and out of our lungs is facilitated by the diaphragm and the intercostal muscles, which are located between our ribs. Here's how it works:

1. Inhalation (Breathing In): When we breathe in, our diaphragm contracts and moves downward. This increases the space in our chest cavity, into which our lungs expand. The intercostal muscles help in this process by moving the rib cage upward and outward, further increasing this space. This decrease in pressure allows outside air to flow into our lungs.

2. Exhalation (Breathing Out): When we breathe out, the diaphragm relaxes and moves upward into the chest cavity. The intercostal muscles also relax, causing the rib cage to move downward and inward. This decreases the space for our lungs, and increases the pressure, which forces air out.

So, even though our lungs themselves do not have muscles, they are able to move air in and out with the help of the diaphragm and intercostal muscles.