Intercostal Muscles

What Are the Intercostals

Intercostals are skeletal muscles located in the intercostal spaces between the ribs in the human body. They belong to the intrinsic chest muscles along with the subcostal, levatores costarum, transversus thoracis, and serratus posterior muscles. In intercostals assist in breathing, especially during forced inhalation and exhalation, and are considered accessory respiratory muscles.

Intercostal Muscle Names with Basic Anatomy and Structure

All the intercostal muscles are divided into the external, internal, and innermost layers. Both the external and internal layers have 22 muscles, 11 on each side of the ribcage. The table below gives a comparison of the three groups to understand their anatomy better:

Muscle	Origin	Insertion	Direction of Muscle Fibers	Action	Innervation	Blood Supply
External Intercostals	Inferior border of the 1st to 11th ribs	Superior border of the corresponding rib below (2nd to 12th)	Inferior to Superior	Elevating the ribs to help increase thoracic volume and facilitate inhalation, especially during forced breathing. Also, stabilizing the ribcage.	Intercostal nerves (T1-T11)	Intercostal arteries
Internal Intercostals	Infero-lateral border of the costal groove of 1st to 11th ribs	Superior border of the corresponding rib below (2nd to 12th)	Superior to Inferior	The opposite of the external intercostals — depressing the ribs to help reduce the thoracic volume to assist in exhalation, especially during forced breathing. Also, stabilizing the ribcage.	Intercostal nerves (T1-T11)	Intercostal arteries
Innermost Intercostals	Inner surface of the 1st to 11th ribs	Superior border of the corresponding rib below (2nd to 12th)	Typically similar to that of internal intercostals, but may vary to some extent	Keeping the ribcage stable during breathing, and aiding in depressing the ribs to facilitate exhalation. Also, maintaining a constant contraction to stabilize the chest wall.	Intercostal nerves (T1-T11)	Intercostal arteries

So, the external and internal intercostal muscles function antagonistically, working together to elevate and depress the ribs. This action expands and compresses the thoracic cavity during inhalation and exhalation. The subcostals, and transversus thoracic muscle also work with these two to control the movement of the rib cage.

Finally, the intercostals play a vital role in maintaining the integrity of the rib cage and thoracic wall, keeping it from collapsing or letting the organs located here bulge out.