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Intercostal muscles
Intercostal muscles highlighted in dark red.
Details
Origin	Ribs 1–11
Insertion	Ribs 2–12
Artery	Intercostal arteries
Nerve	Intercostal nerves
Actions	Elevation or depression of the ribs
Identifiers
Latin	musculi intercostales
MeSH	D007366
FMA	13354
Anatomical terms of muscle [edit on Wikidata]

Theintercostal muscles comprise many different groups ofmuscles that run between theribs, and help form and move thechest wall. The intercostal muscles are mainly involved in the mechanical aspect ofbreathing by helping expand and shrink the size of thechest cavity.^[1]

There are three principal layers:

1. External intercostal muscles also known as intercostalis externus aid in quiet and forcedinhalation. 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 bending them more open, thus expanding the transverse dimensions of thethoracic cavity. The muscle fibers are directed downwards, forwards and medially in the anterior part.
2. Internal intercostal muscles also known as intercostalis internus aid in forcedexpiration (quiet expiration is a passive process). They originate on ribs 2–12 and have their insertions on ribs 1–11.Their fibers pass anterior and superior from the upper margin of the rib and costal cartilage to the lower margin of the rib above.^[2] The internal intercostals are responsible for the depression of the ribs and bending them inward, thus decreasing the transverse dimensions of the thoracic cavity. The muscle fibers are directed downwards, forwards and laterally forming right angle with external intercostal muscle.
3. Innermost intercostal muscle also known as intercostalis intimus are deep layers of the internal intercostal muscles which are separated from them by aneurovascular bundle. The muscle fibers are directed downwards, forwards and laterally same as intercostalis internus muscle.^[3]

Both the external and internal muscles are innervated by theintercostal nerves^[3](theventral rami ofthoracic spinal nerves), are supplied by theintercostal arteries, and are drained by theintercostal veins. Their fibers run in opposite directions.

Thescalene muscles, which also move the chest wall and have a function in inhalation, are also intercostal muscles, just not one of the three principal layers.

• Thoracic diaphragm, another muscle importantly involved in respiratory action.
• Exhalation
• Inhalation

Wikimedia Commons has media related toIntercostal muscles.

• Anatomy figure: 18:03-03 at Human Anatomy Online, SUNY Downstate Medical Center
• UCC
• Gray's Anatomy 41st Edition

• Muscles of the torso

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