Understanding the internal and external intercostal muscles
The internal and external intercostal muscles are very important muscles for respiration. This is true both because of their ability to assist us as we inhale and exhale, and also because of their ability to restrict our ability to breathe! If they are tight, their tension can restrict the ability of the ribs to move apart from one another, which is of course required for inhalations.
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What do the names, internal and external intercostal muscles, mean?
Internal comes from the Latin word internus, which means within. And, external means outside of. The word intercostal comes from the Latin words inter, which means between, and costa, which means rib.
The internal intercostals then, are muscles between the ribs and located inside a structure. In contrast, the external intercostals are muscles between the ribs and located on the outside of a structure. In the case of the intercostals, they are internal or external relative to one another.
Where do the internal and external intercostal muscles attach?
The internal intercostals originate and insert between adjacent ribs. The external intercostals originate on the inferior border of the rib above.
The external intercostals insert on the superior border of the rib below.
What actions do the internal and external intercostal muscles do?
The internal intercostals bring the ribs down during forced expiration. The external intercostals elevate the ribs in inspiration. Keep in mind that the abdominal muscles all have a role to play in forced exhalation.