From Wikipedia, the free encyclopedia
Muscle groups between the ribs which form and move the chest wall during breathing
The
intercostal muscles
comprise many different 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
by helping expand and shrink the size of the
chest cavity
.
[1]
Structure
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There are three principal layers;
- External intercostal muscles
also known as intercostalis externus 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 bending them more open, thus expanding the transverse dimensions of the
thoracic cavity
. The muscle fibers are directed downwards, forwards and medially in the anterior part.
- Internal intercostal muscles
also known as intercostalis internus aid in forced
expiration
(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.
- Innermost intercostal muscle
also known as intercostalis intimus are deep layers of the internal intercostal muscles which are separated from them by a
neurovascular bundle
. The muscle fibers are directed downwards, forwards and laterally same as intercostalis internus muscle.
[3]
Nerve supply
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Both the external and internal muscles are innervated by the
intercostal nerves
[3]
(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.
Function
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The
scalene 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.
See also
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References
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External links
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