|Deep muscles of the chest and front of the arm, with the boundaries of the axilla|
|Gray's||subject #117 403|
|Actions||Elevation or Depression of the Ribs|
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing. These muscles help expand and shrink the size of the chest cavity when you breathe.
There are three principal layers;
- external intercostal muscles aid in quiet and forced inhalation. They originate on ribs 1-11 and have their insertion on ribs 2-12. The external intercostals are responsible for the elevation of the ribs, and expanding the transverse dimensions of the thoracic cavity.
- internal intercostal muscles aid in forced expiration (quiet expiration is a passive process). They originate on ribs 2-12 and have their insertions on ribs 1-11. The internal intercostals are responsible for the depression of the ribs decreasing the transverse dimensions of the thoracic cavity.
- innermost intercostal muscle, the deep layers of the internal intercostal muscles which are separated from them by a neurovascular bundle. This in turn is composed of:
Both the external and internal muscles are innervated by the intercostal nerves (the ventral rami of thoracic spinal nerves), are supplied by the intercostal arteries, and are drained by the intercostal veins. Their fibers run in opposite directions.
The scaleni, which also move the chest wall and have a function in inhalation, are also intercostal muscles, just not one of the three principal layers.
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