Muscles give shape to our body and fill in the whole skeletal frame. Depending upon the requirement, there are various types of muscles which perform varied function to fulfill the needs of that particular organ or part where they are present. Research has proved that there is as strong connection between the muscles, nerves, ligaments and tendons and injury to one can cause abnormalities in the functioning of the other. Just like every organ our respiratory system too comprise of several muscles. Intercoastal muscles are an integral part of it.
Galen was the first researcher who took interest in the working and functioning of intercoastal muscles. He was of the belief that the internal intercostals muscles were engaged in inspiratory functions whereas external intercostals muscles were involved in expiratory. This thought was carried forward for long time until around 1300 years later, Vesalius stated that both the internal as well as the external intercoastal muscles fulfilled the same function. Around 1673, Thomas Willis from Oxford for the first time bifurcated external intercoastal muscles as inspiratory and the internal muscles as only expiratory. Hamberger in 1748 devised a world famous model which supported this theory.
Intercoastal muscles are of two types: External and internal. These are located in betweenthe ribs. The internal intercoastal muscles is placed inside the ribcase and travels from the rib front , around the back moving along the ribs’ bend. The external intecoastal muscles which are placed on the outer surface of the ribcase, moves around ribs back and reach the bony end part of frontal rib. Both the external as well as the internal intercoastal muscles are each present in pairs of eleven.
When there is depression in the diaphragm and simultaneously the ribs get elevated, inspiration by the intercoastal muscles is caused. The process of expiration is the result of thorax weight, lung elasticity and slackening of muscles. The special depressor present in the ribs is trinagularis stemi.
The Internal Intercostals muscles are placed perpendicular to the external intercoastal muscles. Both the internal intercoastal muscles and the external intercoastal muscles work differently. The internal intercoastal muscles or the intercartilagious muscle stretches the ribs so that they are pulled up and higher volume for lung is created due to which lungs can breathe in more air. Thus, these internal muscles perform the function like the extrinsic muscles. During the working, when the muscles shorten and contract, the rib is lifeted. This working can be compared with the transverses thoracais muscles. The only thing of difference is the internal intercoastals escalate the ribs whereas the transverses throacis perform the work of depressing them. This is the working of the internal intercoastal muscles which are inside the rib cage.
The internal intercoastals which are present in the bony rib part are called as the interosseous internal intercoastal muscles. These muscles perform the function of counteracting the activity of external intercoastals. When these muscles shorten or contract, the ribs come closer due to which a positive air pressure is developed between the lung air and the air present outside. The internal intercoastal muscles are hence associated with the functioning of exhalation.
The External Intercostals also perform its work by shortening and contracting. When the muscles contract and shorten, the rib is raised thereby enhancing the lung volume due to which negative pressure difference is built up. The external intercoastal muscles are known help the lungs with inhalation.