Intercostal muscle
From Free net encyclopedia
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall.
There are two principle layers;
- the external intercostal muscles, which aid in inhalation.
- the internal intercostal muscles, which aid in expiration (which is not entirely an active process).
Their fibers run in opposite directions.
The external intercostal muscles 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 cavity.
The internal intercostal muscles originate on ribs 1-11 and have their insertions on ribs 2-12. The internal intercostals are responsible for the depression of the ribs decreasing the transverse dimensions of the thoracic cavity.
Both these muscles are innervated by the intercostal nerves (=ventral rami of thoracic spinal nerves), and are provided by the intercostal arteries and veins.
Besides the scaleni, who also move the chest wall and have a function in inhalation, other intercostal muscles are: