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Intercostal muscles are several groups of
muscleMuscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s 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;
- the external intercostal muscles, which aid in quiet and forced inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....
. 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 cavityThe thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....
.
- the internal intercostal muscles, which aid in forced expiration
Expiration is an independent feature film written, directed and starring Gavin Heffernan. It was the winner of the Grand Jury Prize and Best Film at the Canadian Filmmakers' Festival....
(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 innermost intercostal muscle is a layer of intercostal muscles deep to the plane that contains the intercostal nerves and intercostal vessels and the internal intercostal muscles...
, the deep layers of the internal intercostal muscles which are separated from them by the neurovascular bundleA Neurovascular bundle is a term applied to the body nerves, arteries, veins and lymphatics that tend to travel together in the body...
. This in turn is composed of:
- transversus thoracis muscle
The transversus thoracis lies internal to the thoracic cage, anteriorly. It is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest...
- intercostal space
The intercostal space is the space between two ribs . Since there are 12 ribs on each side, there are 11 intercostal spaces, each numbered for the rib superior to it.-Structures in intercostal space:* several kinds of intercostal muscle...
- subcostalis muscle
Both the external and internal muscles are innervated by the
intercostal nervesThe intercostal nerves are the anterior divisions of the thoracic spinal nerves from T1 to T11.Each nerve is connected with the adjoining ganglion of the sympathetic trunk by a gray and a white ramus communicans...
(the ventral rami of thoracic spinal nerves), and are provided by the
intercostal arteriesThe intercostal arteries are a group of arteries that supply the area between the ribs , called the intercostal space.* Highest intercostal artery - first and second intercostal spaces...
and
intercostal veinsThe intercostal veins are a group of veins which drain the area between the ribs , called the intercostal space.They can be divided as follows:* Anterior intercostal veins* Posterior 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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