Intercostal muscles are many different groups of

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

s 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 Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen. All aerobic creatures need oxygen for cell ...

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. Ther ...

Structure

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 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. #

Internal intercostal muscles The internal intercostal muscles (intercostales interni) are a group of skeletal muscles located between the ribs. They are eleven in number on either side. They commence anteriorly at the sternum, in the intercostal spaces between the cartila ...

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 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. #

Innermost intercostal muscle The innermost intercostal muscle is a layer of intercostal muscles. It may also be called the intima of the internal intercostal muscles. It is the deepest muscular layer of the thorax, with muscle fibres running vertically (in parallel with the ...

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), are supplied by the intercostal arteries, and are drained by the

intercostal veins The intercostal veins are a group of veins which drain the area between the ribs ("costae"), called the intercostal space. They can be divided as follows: * Anterior intercostal veins * Posterior intercostal veins ** Posterior intercost vein that ...

. 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.

References

External links

*
UCC
* Gray's Anatomy 41th Edition {{Muscles of thorax and back Muscles of the torso

Structure

Nerve supply

Function

See also

References

External links