Intercostal muscle

Intercostal muscles are several 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. These muscles help expand and shrink the size of the chest cavity to facilitate breathing.

Intercostal Muscle
Intercostal muscles highlighted in dark red.
Details
Origin	ribs 1-11
Insertion	ribs 2-12
Artery	intercostal arteries
Nerve	intercostal nerves
Actions	Elevation or Depression of the Ribs
Identifiers
Latin	Musculi intercostales
MeSH	D007366
FMA	13354
Anatomical terms of muscle

Structure

There are three principal layers;

1. External intercostal muscles 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.
2. Internal intercostal muscles 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.(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.
3. Innermost intercostal muscle, the deep layers of the internal intercostal muscles which are separated from them by a neurovascular bundle.

Nerve supply

Both the external and internal muscles are innervated by the intercostal nerves (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

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

This article uses anatomical terminology.

• Thoracic diaphragm, another muscle importantly involved in breathing action.
• Exhalation
• Inhalation

External links

• Anatomy figure: 18:03-03 at Human Anatomy Online, SUNY Downstate Medical Center
• UCC