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From Wikipedia, the free encyclopedia

Intercostal muscle
Deep muscles of the chest and front of the arm, with the boundaries of the axilla.
Gray's subject #117 403
Origin ribs 1-11
Insertion    ribs 2-12
Artery intercostal arteries
Nerve intercostal nerves
Actions Elevation or Depression of the Ribs
MeSH Intercostal+Muscles

Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall.

There are three principal layers;

  • the external intercostal muscles, which 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.

Located around the ribs

  • the internal intercostal muscles, which 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.
  • the innermost intercostal muscle, the deep layers of the internal intercostal muscles which are separated from them by the neurovascular bundle.

Both the external and internal muscles are innervated by the intercostal nerves (the ventral rami of thoracic spinal nerves), and are provided by the intercostal arteries and intercostal veins. Their fibers run in opposite directions.

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