Internal intercostal muscles

Internal intercostal muscles
Internal intercostal muscles (red) seen from back.
Details
Latin	Musculi intercostales interni
Origin	Rib - superior border
Insertion	Rib - inferior border
Artery	Intercostal arteries
Nerve	Intercostal nerves
Actions	Hold ribs steady
Antagonist	External intercostal muscles
Identifiers
Dorlands /Elsevier	m_22/12549376
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terms of muscle [[[d:|edit on Wikidata]]]

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 cartilages of the true ribs, and at the anterior extremities of the cartilages of the false ribs, and extend backward as far as the angles of the ribs, whence they are continued to the vertebral column by thin aponeuroses, the posterior intercostal membranes.

Structure

A cutout of the thoracic wall showing the three layers of intercostal muscle - from the left wall.

Each muscle arises from the ridge on the inner surface of a rib, as well as from the corresponding costal cartilage, and is inserted into the inferior border of the rib above. The internal intercostals are innervated by the intercostal nerve.

Their fibers are also directed obliquely, but pass in a direction opposite to those of the external intercostal muscles.

For the most part, they are muscles of exhalation. In exhalation the interosseous portions of the internal intercostal muscles, (the part of the muscle that is between the bone portion of the superior and inferior ribs), depresses and retracts the ribs, compressing the thoracic cavity and expelling air. The internal intercostals, however, are only used in forceful exhalation such as coughing or during exercise and not in relaxed breathing. The external intercostal muscles, and the intercartilaginous part of the internal intercostal muscles, (the part of the muscle that lies between the cartilage portion of the superior and inferior ribs), are used in inspiration, by aiding in elevating the ribs and expanding the thoracic cavity.

Additional images

• 

  Position of internal intercostal muscles (red). Animation.

• 

  Posterior surface of sternum and costal cartilages, showing Transversus thoracis. (Intercostalis internus visible at left.)

• 

  A central rib of the left side. Inferior aspect.

• 

  The Obliquus internus abdominis.

• 

  Diagram of the course and branches of a typical intercostal nerve.

• 

  Thoracic portion of the sympathetic trunk.

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

External links

• -254803891 at GPnotebook
• Anatomy photo:18:03-0101 at the SUNY Downstate Medical Center - "The Internal Intercostal Muscle"
• Anatomy figure: 18:03-03 at Human Anatomy Online, SUNY Downstate Medical Center - "Transverse section of thorax."