Answer:
Intercostal Muscles Overview
In humans, the muscles are solely for the purpose of expanding and contracting the rib cage. Other animals may have slightly different uses for the intercostal muscles, as discussed in the examples below. While the muscles serve generally the same purpose, they have been adapted in various ways in different organisms. These muscles are considered skeletal muscles.
There are 3 types of intercostal muscle. The innermost intercostal lies inside the ribs. The internal intercostal muscle sits between two ribs. The external intercostal muscles sit on the outside of the ribs. Between each of the 12 ribs, each of these three intercostal muscles is present. The first and last ribs only have intercostal muscles on one side.
The intercostal muscles relax while the lungs are expanding, allowing them to fill up with air. When an organism breathes out, the intercostal muscles contract to put pressure on the lungs and help drive the air out. This cycle continues constantly as an organism breathes.
The innermost intercostal muscles relax, while the external intercostal muscles contract, causing the chest cavity to expand. This expansion allows the lungs to fill with air, due to the negative pressure created by the extra space. Air fills the lungs, gases are exchanged, and it is time to exhale.
Step-by-step explanation:
Chest Cavity Contraction
To force the air out, the chest cavity must become smaller, to put pressure on the air. To do this, the opposite process of inhalation happens. The diaphragm and external intercostal muscles contract, applying force to the bottom and sides of the lungs. The innermost intercostal muscles now contract, while the external intercostal muscles relax. This causes the chest cavity to contract as a whole, forcing the air out of your lungs. The internal intercostal muscles, or middle layer of muscle, helps keep the ribs from separating and holds the shape of the chest cavity.
Examples of Intercostal Muscles
Intercostal Muscles in Snakes
In different animals, intercostal muscles can perform different tasks. Snakes use their intercostal muscles in a different way than humans, based on their anatomy. Snakes typically only have one functioning lung, which fills along part of their body. Essentially, a snake has reduced its functional skeleton to a spine and rib cage. As in humans, the intercostal muscles in a snake play a role in bringing air into the lungs. By a similar process, the innermost and external intercostal muscles alternate their contracting and relaxing to expand and contract the lung.
Snakes, having no limbs, must also use their intercostal muscles when making a variety of other movements. While they have layers of muscles on top of their ribs that control their motion, the intercostal muscles have a much larger role to play in maintaining the shape and size of the body cavity.
For instance, when a constricting a prey item, a large snake creates an enormous amount of pressure with their muscles. This pressure is exerted not only on the prey item but also on the snake’s own body. To keep itself from damaging its internal organs, the snake must contract its intercostal muscles and create a strong cage around its lung, heart, and other sensitive organs.