Intercostal muscles are many different groups of
muscles that run between the
ribs
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi- ...
, 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
The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...
.
Structure
There are three principal layers;
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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 thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...
. The muscle fibers are directed downwards, forwards and medially in the anterior part.
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Internal intercostal muscles also known as intercostalis internus aid in forced
expiration
Expiration or expiration date may refer to:
Expiration
Expiration may refer to:
*Death
*Exhalation of breath, breathing out
*Expiration (options), the legal termination of an option to take an action
*Shelf life, or the time after which a product ...
(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 abov
(source)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.
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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.
Nerve supply
Both the external and internal muscles are innervated by the
intercostal nerves (the
ventral rami
The ventral ramus (pl. ''rami'') (Latin for ''branch'') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami.
Shortly after a spinal ...
of
thoracic spinal nerves
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into th ...
), are supplied by the
intercostal arteries, and are drained by the
intercostal veins. Their fibers run in opposite directions.
Function
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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Thoracic diaphragm
The thoracic diaphragm, or simply the diaphragm ( grc, διάφραγμα, diáphragma, partition), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the m ...
, another muscle importantly involved in respiratory action.
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Exhalation
Exhalation (or expiration) is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing.
This happens due to elastic properties of the lungs, ...
*
Inhalation
References
External links
*
UCC*
Gray's Anatomy 41th Edition
{{Muscles of thorax and back
Muscles of the torso